I have used Moisture Cure in the past and usually try to discourage it’s use to customers whenever I am asked to use it. Recently, I was asked by a customer who had a 14 month old girl living in the house and I was trying to inform him the dangers of using Moisture Cure and its harmful VOC’s and dangerous off gassing. Especially to young children (as they are lower to the floor). I mentioned one incident I read about, which happened in an Hasidic Jewish neighborhood in Brooklyn – where Rabbis had to pass out flyers door-to-door about the dangers of using Moisture Cure in the home. The VOCs released from Moisture Cure has been linked to cancer, reproductive problems,asthma and other respiratory issues.
I have used Moisture Cure in the past and usually try to discourage it’s use to customers whenever I am asked to use it. Recently, I was asked by a customer who had a 14 month old girl living in the house and I was trying to inform him the dangers of using Moisture Cure and its harmful VOC’s and dangerous off gassing. Especially to young children (as they are lower to the floor). I mentioned one incident I read about, which happened in an Hasidic Jewish neighborhood in Brooklyn – where Rabbis had to pass out flyers door-to-door about the dangers of using Moisture Cure in the home. The VOCs released from Moisture Cure has been linked to cancer, reproductive problems,asthma and other respiratory issues.
קוק וואו זיין מקור איז.. די צעטלעך אויף די ברוקלינער גאסן! טאקע א שטארקע מקור!
ווען איר האלט ביים מאכען רענאוועשען אין אייר דירה האלט אייך צו די פראדאקטען וואס זענען נידריגע voc low אדער 0 voc עד איז דא אן ארגענעזעשאן וואס ריפט זיך Greengaurd זיי טוען נאר אפראווען די זאכען וואס זענען סעיף.
Volatile Organic Compounds in Your Home
Volatile Organic Compounds (VOCs) are a large group of carbon-based chemicals that easily evaporate at room temperature. While most people can smell high levels of some VOCs, other VOCs have no odor. Odor does not indicate the level of risk from inhalation of this group of chemicals. There are thousands of different VOCs produced and used in our daily lives. Some common examples include:
Acetone Benzene Ethylene glycol Formaldehyde Methylene chloride Perchloroethylene Toluene Xylene 1,3-butadiene Where do VOCs come from?
Many products we have in our homes release or “off-gas” VOCs. Some examples of sources of VOCs are:
Building Materials
Carpets and adhesives Composite wood products Paints Sealing caulks Solvents Upholstery fabrics Varnishes Vinyl Floors Home and Personal Care Products
Air fresheners Air cleaners that produce ozone Cleaning and disinfecting chemicals Cosmetics Fuel oil, gasoline Moth balls Vehicle exhaust running a car in an attached garage Behaviors
Cooking Dry cleaning Hobbies Newspapers Non-electric space heaters Photocopiers Smoking Stored paints and chemicals Wood burning stoves Studies have shown that the level of VOCs indoors is generally two to five times higher than the level of VOC’s outdoors. VOC concentrations in indoor air depend on many factors, including the:
Amount of VOCs in a product; Rate at which the VOCs are released; Volume of the air in the room/building; Ventilation rate or the area; and Outdoor concentrations of VOCs. What are the health effects of VOC exposure?
The risk of health effects from inhaling any chemical depends on how much is in the air, how long and how often a person breathes it in. Scientists look at short-term (acute) exposures as hours to days or long-term (chronic) exposures as years to even lifetime.
Breathing low levels of VOCs for long periods of time may increase some people’s risk of health problems. Several studies suggest that exposure to VOCs may make symptoms worse in people who have asthma or are particularly sensitive to chemicals. These are much different exposures than occupational exposures to VOCs.
VOCs refer to a group of chemicals. Each chemical has its own toxicity and potential for causing different health effects. Common symptoms of exposure to VOCs include:
Short-Term (Acute) to high levels of VOCs
Eye, nose and throat irritation Headaches Nausea / Vomiting Dizziness Worsening of asthma symptoms Long-Term (Chronic) to high levels of VOCs
Increased risk of:
Cancer Liver damage Kidney damage Central Nervous System damage What levels of VOCs is safe?
The best health protection measure is to limit your exposure to products and materials that contain VOCs when possible. If you think you may be having health problems caused by VOCs, try reducing levels in your home. If symptoms persist, consult with your doctor to rule out other serious health conditions that may have similar symptoms
Create a safer environment for your family by using natural or low-VOC paints in your home.
Avoid toxic chemicals in paint by choosing safe paint for lower health risks.
I have to admit that I like the smell of fresh paint. Having lived in a collection of motley old apartments and homes, I loved the way a couple of gallons covered over the scuffs and stains left by the last tenants and created a "new" living space. To me, the aroma of freshly painted walls signified a clean start. But as it turns out, what my nose didn't know could have been hurting me.
That "new-paint smell" is caused by volatile organic compounds (VOCs), a class of chemicals that evaporate readily at room temperature. These toxic chemicals in paint are found in some pigments and also are added to alkyd oil and (to a lesser extent) latex paints to provide certain desirable working qualities, like spreadability, or to improve durability. Low-level exposure to these chemicals may cause temporary health problems, such as headaches, dizziness or nausea. Higher exposure levels, such as with auto spray booth operators, and longer exposure times can cause permanent damage to the kidneys, liver, and nervous or respiratory systems.
To address some of these problems, more than 20 companies now manufacture low- and no-VOC paints that perform as well as their predecessors. A number of paint products can give your home a fresh start without compromising your health. Here's an overview of some low- and noVOC paints, and a few all-natural options you can choose from for both interior and exterior painting projects.
Stick With Latex Paint
Although it can be made up of hundreds of different chemicals, paint still can be divided into two subcategories according to its primary solvent. In latex paints, water is the primary solvent; in alkyds, it's a petroleum solvent (oil). Latex paints, with much lower levels of VOCs, beat alkyds hands-down for safety. (Even the newly formulated alkyd paints use much more solvent than standard latex paints, and cleaning up brush es, rollers and spills after painting with alkyds requires additional solvents—latex paints clean up with soap and water.)
The biggest difference you may notice is with drying time: Low- and no-VOC paints dry a lot faster, and you'll need to work quickly so that you're always painting into a wet edge (painting over dried paint will leave a striped appearance). Because these paints tend to dry faster on rollers and brushes, cleanup may take a little longer.
The Low-Down on Low-VOCs Paint
First, don't confuse "low-odor" with "lowVOC." Fumes from some VOCs can be masked to make a low-odor paint, which means that what you can't smell still can hurt you.
And don't assume that all low-VOC paints are created equal. A "low-VOC" label on a can means the paint meets the EPA's maximum VOC-emission standards: Latex paints must contain less than 250 grams per liter (gm/l) of VOCs; alkyds can contain up to 380 gm/l.
When shopping for a safer paint, start by reading the label. Look for paints that have VOC levels of 150 gm/l or lower. Realize that pigments, typically dissolved in chemical solvents, and other additives, such as mildewcides and conditioners, contribute to the relative toxicity of the final paint mix.
In addition to choosing a low-VOC paint, pay attention to everything else that's in the can. Because the EPA's regulations primarily focus on reducing air pollution, other toxic chemicals that do not increase air pollution, such as heavy metals, are excluded from VOC calculations.
Besides solvents, heavy metals and crystalline silica (beach sand) are added to paint for color or texture. These ingredients aren't a problem when suspended in liquid paint, but they are considered carcinogens if inhaled (which can occur when sanding or scraping). Ammonia is used to inhibit bacteria and mold, and to help the paint "flow" off the brush or roller. And although none of the major paint companies use lead or mercury anymore, paints with mildewcide additives still contain trace amounts of formaldehyde. Formaldehyde is a respiratory irritant and potential carcinogen.
For this reason, chemically sensitive individuals need to be especially careful about using kitchen and bath paints that contain extra mildewcides.
Request a Material Safety Data Sheet (MSDS) from the paint store to get information on everything that goes into the paint. If the store can't provide one, check the manufacturer's Web site or call their customer help line.
All Natural Paint Solutions
Vibrantly colored paints predate modern VOC-based paints by several centuries. The old painted walls of many buildings in Italy, Egypt and Greece attest to the fact that combinations of natural resins, oils, clays, and mineral or plant pigments can be both durable and lightfast. Today, companies such as Bioshield and Sinan have refined those ancient recipes to offer a no-VOC line of plant- and earth-based paints and finishes. (The Old Fashioned Milk Paint Company offers a casein, or milk, paint made from a mixture of lime, earth pigments and milk protein.) Because you mix them yourself, these products offer more artistic creativity. They can be applied full-strength for regular coverage, or thinned to produce a washed effect.
Because natural paints don't use the same solvents that give other paints smoothness and uniformity, they can be a little trickier to apply and tend to give walls a more handcrafted appearance. Natural paints are sometimes sold as a powder, or the pigment is sold separately from a liquid base, requiring you to do the mixing. In these cases, you'll want to make enough for one full coat: Exactly matching one batch to the next is nearly impossible.
Natural paints are not always compatible with other paint products. Milk paint works well on new wood and plaster, but can pull off old paint if it's not adhered well. Milk paints applied over latex binder (used in drywall joint compound) may "crackle." Some natural paints also waterspot easily. For walls or furniture that require extra protection, you may need to apply a topcoat of varnish or polyurethane, which means an extra step and the potential for additional chemical exposure
Dried green paint Paint is any liquid, liquefiable, or mastic composition that, after application to a substrate in a thin layer, converts to a solid film. It is most commonly used to protect, color, or provide texture to objects. Paint can be made or purchased in many colors—and in many different types, such as watercolor, synthetic, etc. Paint is typically stored, sold, and applied as a liquid, but dries into a solid.
History Edit
A charcoal and ochre cave painting of Megaloceros from Lascaux, France. In 2011, South African archeologists reported finding a 100,000-year-old human-made ochre-based mixture that could have been used like paint.[1]Cave paintings drawn with red or yellow ochre, hematite, manganese oxide, and charcoal may have been made by early Geder as long as 40,000 years ago.
A piece of Giant clam shell used to hold ochre paint in pre-dynastic ancient Egypt Ancient colored walls at Dendera, Egypt, which were exposed for years to the elements, still possess their brilliant color, as vivid as when they were painted about 2,000 years ago. The Egyptians mixed their colors with a gummy substance, and applied them separately from each other without any blending or mixture. They appear to have used six colors: white, black, blue, red, yellow, and green. They first covered the area entirely with white, then traced the design in black, leaving out the lights of the ground color. They used minium for red, and generally of a dark tinge.
Pliny mentions some painted ceilings in his day in the town of Ardea, which had been done prior to the foundation of Rome. He expresses great surprise and admiration at their freshness, after the lapse of so many centuries.
Paint was made with the yolk of eggs and therefore, the substance would harden and adhere to the surface it was applied to. Pigment was made from plants, sand, and different soils. Most paints used either oil or water as a base (the dilutant, solvent or vehicle for the pigment).
A still extant example of 17th-century house oil painting is Ham House in Surrey, England, where a primer was used along with several undercoats and an elaborate decorative overcoat; the pigment and oil mixture would have been ground into a paste with a mortar and pestle. The process was done by hand by the painters and exposed them to lead poisoning due to the white-lead powder.
In 1718, Marshall Smith invented a "Machine or Engine for the Grinding of Colours" in England. It is not known precisely how it operated, but it was a device that increased the efficiency of pigment grinding dramatically. Soon, a company called Emerton and Manby was advertising exceptionally low-priced paints that had been ground with labour-saving technology:
One Pound of Colour ground in a Horse-Mill will paint twelve Yards of Work, whereas Colour ground any other Way, will not do half that Quantity. By the proper onset of the Industrial Revolution, paint was being ground in steam-powered mills and an alternative to lead-based pigments was found in a white derivative of zinc oxide. Interior house painting increasingly became the norm as the 19th century progressed, both for decorative reasons and because the paint was effective in preventing the walls rotting from damp. Linseed oil was also increasingly used as an inexpensive binder.
In 1866, Sherwin-Williams in the United States opened as a large paint-maker and invented a paint that could be used from the tin without preparation.
It was not until the stimulus of World War II created a shortage of linseed oil in the supply market that artificial resins, or alkyds, were invented. Cheap and easy to make, they also held the color well and lasted for a long time.
Components Edit Binder (or film former) Edit The binder is the film-forming component of paint. It is the only component that must be present if the binder material is suitable for application. Many binders are too thick to be applied and must be thinned. The type of thinner varies with the binder. The thinner is also called the vehicle, because it makes it possible to transfer the binder to the surface with a brush, roller or sprayer. Components listed below are included optionally, depending on the desired properties of the cured film.
A clear paint like a varnish contains primarily the binder and the vehicle plus some dries. If you add pigment to provide color and opacity to a varnish you create an enamel. Enamels therefore contain the three primary type of ingredients found in all paints - 1) binder, 2) vehicle, 3) pigment.
The binder imparts properties such as gloss, durability, flexibility, and toughness.
Binders include synthetic or natural resins such as alkyds, acrylics, vinyl-acrylics, vinyl acetate/ethylene (VAE), polyurethanes, polyesters, melamine resins, epoxy, or oils. Binders can be categorized according to the mechanisms for drying or curing. Although drying may refer to evaporation of the solvent or thinner, it usually refers to oxidative cross-linking of the binders and is indistinguishable from curing. Some paints form by solvent evaporation only, but most rely on cross-linking processes.[2]
Paints that dry by solvent evaporation and contain the solid binder dissolved in a solvent are known as lacquers. A solid film forms when the solvent evaporates, and because the film can re-dissolve in solvent, lacquers are unsuitable for applications where chemical resistance is important. Classic nitrocellulose lacquers fall into this category, as do non-grain raising stains composed of dyes dissolved in solvent and more modern acrylic-based coatings such as 5-ball Krylon aerosol. Performance varies by formulation, but lacquers generally tend to have better UV resistance and lower corrosion resistance than comparable systems that cure by polymerization or coalescence.
The paint type known as Emulsion in the UK and Latex in the USA is a water-borne dispersion of sub-micrometer polymer particles. These terms in their respective countries cover all paints that use synthetic polymers such as acrylic, vinyl acrylic (PVA), styrene acrylic, etc. as binders.[3] The term "latex" in the context of paint in the USA simply means an aqueous dispersion; latex rubber from the rubber tree is not an ingredient. These dispersions are prepared by emulsion polymerization. Such paints cure by a process called coalescence where first the water, and then the trace, or coalescing, solvent, evaporate and draw together and soften the binder particles and fuse them together into irreversibly bound networked structures, so that the paint cannot redissolve in the solvent/water that originally carried it. The residual surfactants in paint, as well as hydrolytic effects with some polymers cause the paint to remain susceptible to softening and, over time, degradation by water. The general term of latex paint is usually used in the USA, while the term emulsion paint is used for the same products in the UK and the term latex paint is not used at all. Paints that cure by oxidative crosslinking are generally single package coatings. When applied, the exposure to oxygen in the air starts a process that crosslinks and polymerizes the binder component. Classic alkyd enamels would fall into this category. Oxidative cure coatings are catalyzed by metal complex driers such as cobalt naphthenate.
Paints that cure by polymerization are generally one or two package coatings that polymerize by way of a chemical reaction, and cure into a crosslinked film. Depending on composition they may need to dry first, by evaporation of solvent. Classic two package epoxies or polyurethanes would fall into this category.[4]
There are paints called plastisols/organosols, which are made by blending PVC granules with a plasticiser. These are stoved and the mix coalesces.
Other films are formed by cooling of the binder. For example, encaustic or wax paints are liquid when warm, and harden upon cooling. In many cases, they resoften or liquify if reheated.
Recent environmental requirements restrict the use of volatile organic compounds (VOCs), and alternative means of curing have been developed, particularly for industrial purposes. In UV curing paints, the solvent is evaporated first, and hardening is then initiated by ultraviolet light. In powder coatings there is little or no solvent, and flow and cure are produced by heating of the substrate after electrostatic application of the dry powder.
Diluent or Solvent Edit The main purposes of the diluent are to dissolve the polymer and adjust the viscosity of the paint. It is volatile and does not become part of the paint film. It also controls flow and application properties, and in some cases can affect the stability of the paint while in liquid state. Its main function is as the carrier for the non volatile components. To spread heavier oils (for example, linseed) as in oil-based interior house paint, a thinner oil is required. These volatile substances impart their properties temporarily—once the solvent has evaporated, the remaining paint is fixed to the surface.
This component is optional: some paints have no diluent.
Water is the main diluent for water-borne paints, even the co-solvent types.
Solvent-borne, also called oil-based, paints can have various combinations of organic solvents as the diluent, including aliphatics, aromatics, alcohols, ketones and white spirit. Specific examples are organic solvents such as petroleum distillate, esters, glycol ethers, and the like. Sometimes volatile low-molecular weight synthetic resins also serve as diluents.
Pigment and Filler Edit Main article: Pigment Pigments are granular solids incorporated in the paint to contribute color. Fillers are granular solids incorporate to impart toughness, texture, give the paint special properties, or to reduce the cost of the paint. Alternatively, some paints contain dyes instead of or in combination with pigments.
Pigments can be classified as either natural or synthetic. Natural pigments include various clays, calcium carbonate, mica, silicas, and talcs. Synthetics would include engineered molecules, calcined clays, blanc fixe, precipitated calcium carbonate, and synthetic pyrogenic silicas.
Hiding pigments, in making paint opaque, also protect the substrate from the harmful effects of ultraviolet light. Hiding pigments include titanium dioxide, phthalo blue, red iron oxide, and many others.
Fillers are a special type of pigment that serve to thicken the film, support its structure and increase the volume of the paint. Fillers are usually cheap and inert materials, such as diatomaceous earth, talc, lime, barytes, clay, etc. Floor paints that must resist abrasion may contain fine quartz sand as a filler. Not all paints include fillers. On the other hand, some paints contain large proportions of pigment/filler and binder.
Some pigments are toxic, such as the lead pigments that are used in lead paint. Paint manufacturers began replacing white lead pigments with titanium white (titanium dioxide), before lead was banned in paint for residential use in 1978 by the US Consumer Product Safety Commission. The titanium dioxide used in most paints today is often coated with silica/alumina/zirconium for various reasons, such as better exterior durability, or better hiding performance (opacity) promoted by more optimal spacing within the paint film.
Additives Edit Besides the three main categories of ingredients, paint can have a wide variety of miscellaneous additives, which are usually added in small amounts, yet provide a significant effect on the product. Some examples include additives to modify surface tension, improve flow properties, improve the finished appearance, increase wet edge, improve pigment stability, impart antifreeze properties, control foaming, control skinning, etc. Other types of additives include catalysts, thickeners, stabilizers, emulsifiers, texturizers, adhesion promoters, UV stabilizers, flatteners (de-glossing agents), biocides to fight bacterial growth, and the like.
Additives normally do not significantly alter the percentages of individual components in a formulation.[5]
Color-changing paint Art Application Product variants Failure of a paint Degradation Dangers See also References Further reading Read in another language Wikipedia<sup>®</sup>® Mobile Desktop Content is available under CC BY-SA 3.0 unless otherwise noted. Terms of Use Privacy
Benzene is an important organic chemical compound with the chemical formula C6H6. Its molecule is composed of 6 carbon atoms joined in a ring, with 1 hydrogen atom attached to each carbon atom. Because its molecules contain only carbon and hydrogen atoms, benzene is classed as a hydrocarbon.
Benzene is a natural constituent of crude oil, and is one of the most elementary petrochemicals. Benzene is an aromatic hydrocarbon and the second [n]-annulene ([6]-annulene), a cyclic hydrocarbon with a continuous pi bond. It is sometimes abbreviated Ph–H. Benzene is a colorless and highly flammable liquid with a sweet smell. It is mainly used as a precursor to heavy chemicals, such as ethylbenzene and cumene, which are produced on a billion kilogram scale. Because it has a high octane number, it is an important component of gasoline, comprising a few percent of its mass. Most non-industrial applications have been limited by benzene's carcinogenicity. Historic benzene formulae as proposed by Kekulé.[10] The word "benzene" derives historically from "gum benzoin" (benzoin resin), an aromatic resin known to European pharmacists and perfumers since the 15th century as a product of southeast Asia.[11] An acidic material was derived from benzoin by sublimation, and named "flowers of benzoin", or benzoic acid. The hydrocarbon derived from benzoic acid thus acquired the name benzin, benzol, or benzene.[12] Michael Faraday first isolated and identified benzene in 1825 from the oily residue derived from the production of illuminating gas, giving it the name bicarburet of hydrogen.[13][14] In 1833, Eilhard Mitscherlich produced it via the distillation of benzoic acid (from gum benzoin) and lime. He gave the compound the name benzin.[15] In 1836, the French chemist Auguste Laurent named the substance "phène";[16] this is the root of the word phenol, which is hydroxylated benzene, and phenyl, which is the radical formed by abstraction of a hydrogen atom (free radical H•) from benzene.
In 1845, Charles Mansfield, working under August Wilhelm von Hofmann, isolated benzene from coal tar.[17] Four years later, Mansfield began the first industrial-scale production of benzene, based on the coal-tar method.[18][19] Gradually the sense developed among chemists that substances related to benzene represent a diverse chemical family. In 1855, Hofmann used the word "aromatic" to designate this family relationship, after a characteristic property of many of its members.[20] In 1997, benzene was detected in deep space.[21]
Ring formula[edit]
Historic benzene formulae (from left to right) by Claus (1867),[22] Dewar (1867),[23] Ladenburg (1869),[24] Armstrong (1887),[25] Thiele (1899)[26] and Kekulé (1865). Dewar benzene and prismane are different chemicals that have Dewar's and Ladenburg's structures. Thiele and Kekulé's structures are used today. The empirical formula for benzene was long known, but its highly polyunsaturated structure, with just one hydrogen atom for each carbon atom, was challenging to determine. Archibald Scott Couper in 1858 and Joseph Loschmidt in 1861[27] suggested possible structures that contained multiple double bonds or multiple rings, but too little evidence was then available to help chemists decide on any particular structure.
In 1865, the German chemist Friedrich August Kekulé published a paper in French (for he was then teaching in Francophone Belgium) suggesting that the structure contained a six-membered ring of carbon atoms with alternating single and double bonds. The next year he published a much longer paper in German on the same subject.[28][29] Kekulé used evidence that had accumulated in the intervening years—namely, that there always appeared to be only one isomer of any monoderivative of benzene, and that there always appeared to be exactly three isomers of every disubstituted derivative—now understood to correspond to the ortho, meta, and para patterns of arene substitution—to argue in support of his proposed structure.[30] Kekulé's symmetrical ring could explain these curious facts, as well as benzene's 1:1 carbon-hydrogen ratio.[31]
The new understanding of benzene, and hence of all aromatic compounds, proved to be so important for both pure and applied chemistry that in 1890 the German Chemical Society organized an elaborate appreciation in Kekulé's honor, celebrating the twenty-fifth anniversary of his first benzene paper. Here Kekulé spoke of the creation of the theory. He said that he had discovered the ring shape of the benzene molecule after having a reverie or day-dream of a snake seizing its own tail (this is a common symbol in many ancient cultures known as the Ouroboros or Endless knot).[32] This vision, he said, came to him after years of studying the nature of carbon-carbon bonds. This was 7 years after he had solved the problem of how carbon atoms could bond to up to four other atoms at the same time. It is curious that a similar, humorous depiction of benzene had appeared in 1886 in the Berichte der Durstigen Chemischen Gesellschaft (Journal of the Thirsty Chemical Society), a parody of the Berichte der Deutschen Chemischen Gesellschaft, only the parody had monkeys seizing each other in a circle, rather than snakes as in Kekulé's anecdote.[33] Some historians have suggested that the parody was a lampoon of the snake anecdote, possibly already well known through oral transmission even if it had not yet appeared in print.[12] (Some others have speculated that Kekulé's story in 1890 was a re-parody of the monkey spoof, and was a mere invention rather than a recollection of an event in his life.[citation needed]) Kekulé's 1890 speech[34] in which these anecdotes appeared has been translated into English.[35] If the anecdote is the memory of a real event, circumstances mentioned in the story suggest that it must have happened early in 1862.[36]
The cyclic nature of benzene was finally confirmed by the crystallographer Kathleen Lonsdale in 1929.[37][38]
Early applications[edit] In the 19th and early-20th centuries, benzene was used as an after-shave lotion because of its pleasant smell. Prior to the 1920s, benzene was frequently used as an industrial solvent, especially for degreasing metal. As its toxicity became obvious, benzene was supplanted by other solvents, especially toluene (methyl benzene), which has similar physical properties but is not as carcinogenic.
In 1903, Ludwig Roselius popularized the use of benzene to decaffeinate coffee. This discovery led to the production of Sanka. This process was later discontinued. Benzene was historically used as a significant component in many consumer products such as Liquid Wrench, several paint strippers, rubber cements, spot removers and other hydrocarbon-containing products. Some ceased manufacture of their benzene-containing formulations in about 1950, while others continued to use benzene as a component or significant contaminant until the late 1970s when leukemia deaths were found associated with Goodyear's Pliofilm production operations in Ohio. Until the late 1970s, many hardware stores, paint stores, and other retail outlets sold benzene in small cans, such as quart size, for general-purpose use. Many students were exposed to benzene in school and university courses while performing laboratory experiments with little or no ventilation in many cases. This dangerous practice has been almost totally eliminated.
Occurrence[edit] Trace amounts of benzene are found in petroleum and coal. It is a byproduct of the incomplete combustion of many materials. For commercial use, until World War II, most benzene was obtained as a by-product of coke production (or "coke-oven light oil") for the steel industry. However, in the 1950s, increased demand for benzene, especially from the growing polymers industry, necessitated the production of benzene from petroleum. Today, most benzene comes from the petrochemical industry, with only a small fraction being produced from coal.[39]
Structure[edit] Main article: Aromaticity
The various representations of benzene X-ray diffraction shows that all six carbon-carbon bonds in benzene are of the same length, at 140 picometres (pm). The C–C bond lengths are greater than a double bond (135 pm) but shorter than a single bond (147 pm). This intermediate distance is consistent with electron delocalization: the electrons for C–C bonding are distributed equally between each of the six carbon atoms. Benzene has 6 hydrogen atoms - fewer than the corresponding parent alkane, hexane. The molecule is planar.[40] The MO description involves the formation of three delocalized π orbitals spanning all six carbon atoms, while the VB description involves a superposition of resonance structures.[41][42][43][44] It is likely that this stability contributes to the peculiar molecular and chemical properties known as aromaticity. To accurately reflect the nature of the bonding, benzene is often depicted with a circle inside a hexagonal arrangement of carbon atoms.
Derivatives of benzene occur sufficiently often as a component of organic molecules that there is a Unicode symbol in the Miscellaneous Technical block with the code U+232C (⌬) to represent it with three double bonds,[45] and U+23E3 (⏣) for a delocalized version.[46]
Benzene derivatives[edit] Main articles: Aromatic hydrocarbons and Alkylbenzenes Many important chemical compounds are derived from benzene by replacing one or more of its hydrogen atoms with another functional group. Examples of simple benzene derivatives are phenol, toluene, and aniline, abbreviated PhOH, PhMe, and PhNH2, respectively. Linking benzene rings gives biphenyl, C6H5–C6H5. Further loss of hydrogen gives "fused" aromatic hydrocarbons, such as naphthalene and anthracene. The limit of the fusion process is the hydrogen-free allotrope of carbon, graphite.
In heterocycles, carbon atoms in the benzene ring are replaced with other elements. The most important derivatives are the rings containing nitrogen. Replacing one CH with N gives the compound pyridine, C5H5N. Although benzene and pyridine are structurally related, benzene cannot be converted into pyridine. Replacement of a second CH bond with N gives, depending on the location of the second N, pyridazine, pyrimidine, and pyrazine.
Production[edit] Four chemical processes contribute to industrial benzene production: catalytic reforming, toluene hydrodealkylation, toluene disproportionation, and steam cracking. According to the ATSDR Toxicological Profile for benzene, between 1978 and 1981, catalytic reformats accounted for approximately 44–50% of the total U.S benzene production.[39]
Catalytic reforming[edit] In catalytic reforming, a mixture of hydrocarbons with boiling points between 60–200 °C is blended with hydrogen gas and then exposed to a bifunctional platinum chloride or rhenium chloride catalyst at 500–525 °C and pressures ranging from 8–50 atm. Under these conditions, aliphatic hydrocarbons form rings and lose hydrogen to become aromatic hydrocarbons. The aromatic products of the reaction are then separated from the reaction mixture (or reformate) by extraction with any one of a number of solvents, including diethylene glycol or sulfolane, and benzene is then separated from the other aromatics by distillation. The extraction step of aromatics from the reformate is designed to produce aromatics with lowest non-aromatic components. Recovery of the aromatics, commonly referred to as BTX (benzene, toluene and xylene isomers), involves such extraction and distillation steps. There are a good many licensed processes available for extraction of the aromatics.
In similar fashion to this catalytic reforming, UOP and BP commercialized a method from LPG (mainly propane and butane) to aromatics.
Toluene hydrodealkylation[edit] Toluene hydrodealkylation converts toluene to benzene. In this hydrogen-intensive process, toluene is mixed with hydrogen, then passed over a chromium, molybdenum, or platinum oxide catalyst at 500–600 °C and 40–60 atm pressure. Sometimes, higher temperatures are used instead of a catalyst (at the similar reaction condition). Under these conditions, toluene undergoes dealkylation to benzene and methane:
C6H5CH3 + H2 → C6H6 + CH4 This irreversible reaction is accompanied by an equilibrium side reaction that produces biphenyl (aka diphenyl) at higher temperature:
2 C 6H 6 is in equilibrium with H 2 + C 6H 5–C 6H 5 If the raw material stream contains much non-aromatic components (paraffins or naphthenes), those are likely decomposed to lower hydrocarbons such as methane, which increases the consumption of hydrogen.
A typical reaction yield exceeds 95%. Sometimes, xylenes and heavier aromatics are used in place of toluene, with similar efficiency.
This is often called "on-purpose" methodology to produce benzene, compared to conventional BTX (benzene-toluene-xylene) extraction processes.
Toluene disproportionation[edit] Where a chemical complex has similar demands for both benzene and xylene, then toluene disproportionation (TDP) may be an attractive alternative to the toluene hydrodealkylation. In the broad sense, 2 toluene molecules are reacted and the methyl groups rearranged from one toluene molecule to the other, yielding one benzene molecule and one xylene molecule.
Given that demand for para-xylene (p-xylene) substantially exceeds demand for other xylene isomers, a refinement of the TDP process called Selective TDP (STDP) may be used. In this process, the xylene stream exiting the TDP unit is approximately 90% paraxylene. In some current catalytic systems, even the benzene-to-xylenes ratio is decreased (more xylenes) when the demand of xylenes is higher.
Steam cracking[edit] Steam cracking is the process for producing ethylene and other alkenes from aliphatic hydrocarbons. Depending on the feedstock used to produce the olefins, steam cracking can produce a benzene-rich liquid by-product called pyrolysis gasoline. Pyrolysis gasoline can be blended with other hydrocarbons as a gasoline additive, or routed through an extraction process to recover BTX aromatics (benzene, toluene and xylenes).
Other methods[edit] Although of no commercial significance, many other routes to benzene exist. Phenol and halobenzenes can be reduced with metals, for example. Benzoic acid and its salts undergo decarboxylation]] to benzene. Via the reaction the diazonium compound with hypophosphorus acid aniline gives benzene. Trimerization of acetylene gives benzene.
Uses[edit] Benzene is used mainly as an intermediate to make other chemicals, above all ethylbenzene, cumene, cyclohexane, nitrobenzene, and alkylbenzene. More than half of the entire benzene production is processed into ethylbenzene, a precursor to styrene, which is used to make polymers and plastics like polystyrene and EPS. Some 20% of the benzene production is used to manufacture cumene, which is needed to produce phenol and acetone for resins and adhesives. Cyclohexane consumes ca. 10% of the world's benzene production; it is primarily used in the manufacture of nylon fibers, which are processed into textiles and engineering plastics. Smaller amounts of benzene are used to make some types of rubbers, lubricants, dyes, detergents, drugs, explosives, and pesticides. In 2013, the biggest consumer country of benzene was China, followed by the USA. Benzene production is currently expanded in the Middle East and in Africa, whereas capacities in Western Europe and North America stagnate.[47]
Toluene is now often used as a substitute for benzene, for instance as a fuel additive. The solvent-properties of the two are similar, but toluene is less toxic and has a wider liquid range. Toluene is also processed into benzene.[47]
Major commodity chemicals and polymers derived from benzene. Clicking on the image loads the appropriate article Component of gasoline[edit] As a gasoline (petrol) additive, benzene increases the octane rating and reduces knocking. As a consequence, gasoline often contained several percent benzene before the 1950s, when tetraethyl lead replaced it as the most widely used antiknock additive. With the global phaseout of leaded gasoline, benzene has made a comeback as a gasoline additive in some nations. In the United States, concern over its negative health effects and the possibility of benzene's entering the groundwater have led to stringent regulation of gasoline's benzene content, with limits typically around 1%.[48] European petrol specifications now contain the same 1% limit on benzene content. The United States Environmental Protection Agency introduced new regulations in 2011 that lowered the benzene content in gasoline to 0.62%.[49]
Reactions[edit] The most common reactions of benzene involve substitution of a proton by other groups.[50] Electrophilic aromatic substitution is a general method of derivatizing benzene. Benzene is sufficiently nucleophilic that it undergoes substitution by acylium ions and alkyl carbocations to give substituted derivatives.
Electrophilic aromatic substitution of benzene The most widely practiced example of this reaction is the ethylation of benzene.
EtC6H5route.png Approximately 24,700,000 tons were produced in 1999.[51] Highly instructive but of far less industrial significance is the Friedel-Crafts alkylation of benzene (and many other aromatic rings) using an alkyl halide in the presence of a strong Lewis acid catalyst. Similarly, the Friedel-Crafts acylation is a related example of electrophilic aromatic substitution. The reaction involves the acylation of benzene (or many other aromatic rings) with an acyl chloride using a strong Lewis acid catalyst such as aluminium chloride or Iron(III) chloride.
Friedel-Crafts acylation of benzene by acetyl chloride Sulfonation, chlorination, nitration[edit] Using electrophilic aromatic substitution, many functional groups are introduced onto the benzene framework. Sulfonation of benzene involves the use of oleum, a mixture of sulfuric acid with sulfur trioxide. Sulfonated benzene derivatives are useful detergents. In nitration, benzene reacts with nitronium ions (NO2+), which is a strong electrophile produced by combining sulfuric and nitric acids. Nitrobenzene is the precursor to aniline. Chlorination is achieved with chlorine to give chlorobenzene in the presence of a catalyst such as aluminium trichloride.
Hydrogenation[edit] Via hydrogenation, benzene and its derivatives convert to cyclohexane and derivatives. This reaction is achieved by the use of high pressures of hydrogen at high temperatures in the presence of a finely divided nickel, which serves as a catalyst. In the absence of the catalyst, benzene is impervious to hydrogen. This reaction is practiced on a very large scale industrially.
Metal complexes[edit] Benzene is an excellent ligand in the organometallic chemistry of low-valent metals. Important examples include the sandwich and half-sandwich complexes, respectively, Cr(C6H6)2 and [RuCl2(C6H6)]2.
Health effects[edit]
A bottle of benzene. The warnings show benzene is a toxic and flammable liquid.[color=#FF4000]
Benzene increases the risk of cancer and other illnesses. Benzene is a notorious cause of bone marrow failure. Substantial quantities of epidemiologic, clinical, and laboratory data link benzene to aplastic anemia, acute leukemia, and bone marrow abnormalities.[52][53] The specific hematologic malignancies that benzene is associated with include: acute myeloid leukemia (AML), aplastic anemia, myelodysplastic syndrome (MDS), acute lymphoblastic leukemia (ALL), and chronic myeloid leukemia (CML)
.[54] [/color]
The American Petroleum Institute (API) stated in 1948 that "it is generally considered that the only absolutely safe concentration for benzene is zero."[55] The US Department of Health and Human Services (DHHS) classifies benzene as a human carcinogen. Long-term exposure to excessive levels of benzene in the air causes leukemia, a potentially fatal cancer of the blood-forming organs. In particular, Acute myeloid leukemia or acute nonlymphocytic leukemia (AML & ANLL) is not disputed to be caused by benzene.[56] IARC rated benzene as "known to be carcinogenic to humans" (Group 1).
Because benzene is ubiquitous in gasoline and hydrocarbon fuels are in use everywhere, human exposure to benzene is a global health problem. Benzene targets liver, kidney, lung, heart and the brain and can cause DNA strand breaks, chromosomal damage, etc. Benzene causes cancer in animals including humans. Benzene has been shown to cause cancer in both sexes of multiple species of laboratory animals exposed via various routes.[57][58]
Some women who inhaled high levels of benzene for many months had irregular menstrual periods and a decrease in the size of their ovaries. Benzene exposure has been linked directly to the neural birth defects spina bifida and anencephaly.[59] Men exposed to high levels of benzene are more likely to have an abnormal amount of chromosomes in their sperm, which impacts fertility and fetal development.[60]
Exposure to benzene[edit] According to the Agency for Toxic Substances and Disease Registry (ATSDR) (2007), benzene is both an anthropogenically produced and naturally occurring chemical from processes that include: volcanic eruptions, wild fires, synthesis of chemicals such as phenol, production of synthetic fibers, and fabrication of rubbers, lubricants, pesticides, medications, and dyes. The major sources of benzene exposure are tobacco smoke, automobile service stations, exhaust from motor vehicles, and industrial emissions; however, ingestion and dermal absorption of benzene can also occur through contact with contaminated water. Benzene is hepatically metabolized and excreted in the urine. Measurement of air and water levels of benzene is accomplished through collection via activated charcoal tubes, which are then analyzed with a gas chromatograph. The measurement of benzene in humans can be accomplished via urine, blood, and breath tests; however, all of these have their limitations because benzene is rapidly metabolized in the human body.[61]
OSHA regulates levels of benzene in the workplace.[62] The maximum allowable amount of benzene in workroom air during an 8-hour workday, 40-hour workweek is 1 ppm. Because benzene can cause cancer, NIOSH recommends that all workers wear special breathing equipment when they are likely to be exposed to benzene at levels exceeding the recommended (8-hour) exposure limit of 0.1 ppm.[63]
Benzene exposure limits[edit] The United States Environmental Protection Agency has set a maximum contaminant level (MCL) for benzene in drinking water at 0.005 mg/L (5 ppb), as promulgated via the U.S. National Primary Drinking Water Regulations.[64] This regulation is based on preventing benzene leukemogenesis. The maximum contaminant level goal (MCLG), a nonenforceable health goal that would allow an adequate margin of safety for the prevention of adverse effects, is zero benzene concentration in drinking water. The EPA requires that spills or accidental releases into the environment of 10 pounds (4.5 kg) or more of benzene be reported.
The U.S. Occupational Safety and Health Administration (OSHA) has set a permissible exposure limit of 1 part of benzene per million parts of air (1 ppm) in the workplace during an 8-hour workday, 40-hour workweek. The short term exposure limit for airborne benzene is 5 ppm for 15 minutes.[65] These legal limits were based on studies demonstrating compelling evidence of health risk to workers exposed to benzene. The risk from exposure to 1 ppm for a working lifetime has been estimated as 5 excess leukemia deaths per 1,000 employees exposed. (This estimate assumes no threshold for benzene's carcinogenic effects.) OSHA has also established an action level of 0.5 ppm to encourage even lower exposures in the workplace.[66]
The U.S. National Institute for Occupational Safety and Health (NIOSH) revised the Immediately Dangerous to Life and Health (IDLH) concentration for benzene to 500 ppm. The current NIOSH definition for an IDLH condition, as given in the NIOSH Respirator Selection Logic, is one that poses a threat of exposure to airborne contaminants when that exposure is likely to cause death or immediate or delayed permanent adverse health effects or prevent escape from such an environment [NIOSH 2004]. The purpose of establishing an IDLH value is (1) to ensure that the worker can escape from a given contaminated environment in the event of failure of the respiratory protection equipment and (2) is considered a maximum level above which only a highly reliable breathing apparatus providing maximum worker protection is permitted [NIOSH 2004[67]].[68] In September 1995, NIOSH issued a new policy for developing recommended exposure limits (RELs) for substances, including carcinogens. Because benzene can cause cancer, NIOSH recommends that all workers wear special breathing equipment when they are likely to be exposed to benzene at levels exceeding the REL (10-hour) of 0.1 ppm.[69] The NIOSH STEL[clarification needed] (15 min) is 1 ppm.
American Conference of Governmental Industrial Hygienists (ACGIH) adopted Threshold Limit Values (TLVs) for benzene at 0.5 ppm TWA and 2.5 ppm STEL.
Toxicology[edit] Biomarkers of exposure[edit] Several tests can determine exposure to benzene. Benzene itself can be measured in breath, blood or urine, but such testing is usually limited to the first 24 hours post-exposure due to the relatively rapid removal of the chemical by exhalation or biotransformation. Most persons in developed countries have measureable baseline levels of benzene and other aromatic petroleum hydrocarbons in their blood. In the body, benzene is enzymatically converted to a series of oxidation products including muconic acid, phenylmercapturic acid, phenol, catechol, hydroquinone and 1,2,4-trihydroxybenzene. Most of these metabolites have some value as biomarkers of human exposure, since they accumulate in the urine in proportion to the extent and duration of exposure, and they may still be present for some days after exposure has ceased. The current ACGIH biological exposure limits for occupational exposure are 500 μg/g creatinine for muconic acid and 25 μg/g creatinine for phenylmercapturic acid in an end-of-shift urine specimen.[70][71][72][73]
Biotransformations[edit] Even if it is not a common substrate for the metabolism, benzene can be oxidized by both bacteria and eukaryotes. In bacteria, dioxygenase enzyme can add an oxygen to the ring, and the unstable product is immediately reduced (by NADH) to a cyclic diol with two double bonds, breaking the aromaticity. Next, the diol is newly reduced by NADH to catechol. The catechol is then metabolized to acetyl CoA and succinyl CoA, used by organisms mainly in the Krebs Cycle for energy production.
The pathway for the metabolism of benzene is complex and begins in the liver. Several enzymes are involved. These include cytochrome P450 2E1 (CYP2E1), quinine oxidoreductase (NQ01), GSH, and myeloperoxidase (MPO). CYP2E1 is involved at multiple steps: converting benzene to oxepin (benzene oxide), phenol to hydroquinone, and hydroquinone to both benzenetriol and catechol. Hydroquinone, benzenetriol and catechol are converted to polyphenols. In the bone marrow, MPO converts these polyphenols to benzoquinones. These intermediates and metabolites induce genotoxicity by multiple mechanisms including inhibition of topoisomerase II (which maintains chromosome structure), disruption of microtubules (which maintains cellular structure and organization), generation of oxygen free radicals (unstable species) that may lead to point mutations, increasing oxidative stress, inducing DNA strand breaks, and altering DNA methylation (which can affect gene expression). NQ01 and GSH shift metabolism away from toxicity. NQ01 metabolizes benzoquinone toward polyphenols (counteracting the effect of MPO). GSH is involved with the formation of phenylmercapturic acid.[54][74]
Genetic polymorphisms in these enzymes may induce loss of function or gain of function. For example, mutations in CYP2E1 increase activity and result in increased generation of toxic metabolites. NQ01 mutations result in loss of function and may result in decreased detoxification. Myeloperoxidase mutations result in loss of function and may result in decreased generation of toxic metabolites. GSH mutations or deletions result in loss of function and result in decreased detoxification. These genes may be targets for genetic screening for susceptibility to benzene toxicity.[75]
Molecular toxicology[edit] The paradigm of toxicological assessment of benzene is shifting towards the domain of molecular toxicology as it allows understanding of fundamental biological mechanisms in a better way. Glutathione seems to play an important role by protecting against benzene-induced DNA breaks and it is being identified as a new biomarker for exposure and effect.[76] Benzene causes chromosomal aberrations in the peripheral blood leukocytes and bone marrow explaining the higher incidence of leukemia and multiple myeloma caused by chronic exposure. These aberrations can be monitored using fluorescent in situ hybridization (FISH) with DNA probes to assess the effects of benzene along with the hematological tests as markers of hematotoxicity.[77] Benzene metabolism involves enzymes coded for by polymorphic genes. Studies have shown that genotype at these loci may influence susceptibility to the toxic effects of benzene exposure. Individuals carrying variant of NAD(P)H:quinone oxidoreductase 1 (NQO1), microsomal epoxide hydrolase (EPHX) and deletion of the glutathione S-transferase T1 (GSTT1) showed a greater frequency of DNA single-stranded breaks.[78]
Biological oxidation and carcinogenic activity[edit] One way of understanding the carcinogenic effects of benzene is by examining the products of biological oxidation. Pure benzene, for example, oxidizes in the body to produce an epoxide, benzene oxide, which is not excreted readily and can interact with DNA to produce harmful mutations.
Routes of exposure[edit] Inhalation[edit] Outdoor air may contain low levels of benzene from automobile service stations, wood smoke, tobacco smoke, the transfer of gasoline, exhaust from motor vehicles, and industrial emissions.[79] About 50% of the entire nationwide (United States) exposure to benzene results from smoking tobacco or from exposure to tobacco smoke.[80]
Inhaled benzene is primarily expelled unchanged through exhalation. In a human study 16.4 to 41.6% of retained benzene was eliminated through the lungs within five to seven hours after a two- to three-hour exposure to 47 to 110 ppm and only 0.07 to 0.2% of the remaining benzene was excreted unchanged in the urine. After exposure to 63 to 405 mg/m3 of benzene for 1 to 5 hours, 51 to 87% was excreted in the urine as phenol over a period of 23 to 50 hours. In another human study, 30% of absorbed dermally applied benzene, which is primarily metabolized in the liver, was excreted as phenol in the urine.[81]
Exposure through smoking[edit] Exposure of the general population to benzene occurs mainly through breathing, the major sources of benzene being tobacco smoke as well as automobile service stations, exhaust from motor vehicles and industrial emissions (about 20% altogether). According to the CDC, "The mean number of cigarettes per day (cpd) among daily smokers in 1993 was 19.6 (21.3 cpd for men and 17.8 cpd for women) and in 2004 was 16.8 (18.1 cpd for men and 15.3 cpd for women)."[82] According to the August 2007 Public Health Statement, the average smoker smokes 32 cpd, which in turn the average smoker would take in about 1.8 milligrams (mg) of benzene per day. This amount is about 10 times the average daily intake of benzene by nonsmokers.[83]
חמירא סכנתא נישט ניצען עפעס וואס האט אין זיך בענזין למשל סעינט מאריטץ וועל דאן אווען קלינער, העגעדי סילווער פאליש וואס האט אין זיך PERC, מויסטשער קיור וואס האט בענזין.
פאר דער וואס פרעגט ווי זענען די דאקטארים אויף דעם ענין עס איז דא כלל אין הלכה אז ווען איין דאקטער זאגט אויף א חולה אז מען ברויך נישט מחלל שבת זיין און איין דאקטער זאגט אז מען ברויך יא מחלל שבת זיין ברויך מען מחלל שבת זיין, צום ענין לויט ווי מען ווייסטוועלכען דאקטער מען פרעגט זאגט אז דאס איז א סם אין מען זאל דאס נישט ניצען[/color], Dr. Patel, Dr. Shakoohi Dr. Seif, Dr. Grusko Dr. Zegelboum, Dr. Rosman, Dr. Statfeled, Dr. Stein פון אלבערט איינסטיין שרייבט די ווערטער "די קעימיקעל מויסטשער קיור יארטעין וואס מען ניצט צו גלאנצען האלטצענע פלארס וואס האט די Toluene Diisocyanate Xylene Ethyl Benzene איז באוויסט אז [color=#FF0000]דאס ברענגט Leukemia, Breast Cancer, Liver, & Kidney Cancer, There is no safe level of exposure to Carcinogens,
[left]says If we stop the use of this dangers chemical moisture cure in the Jewush community, with gods help we can cut the Cancer rate in half[/left]
א וואונדער כ'האב קיינמאל נישט געהערט אז אין אנדערע אידישע ישובים וויא יוראפ אדער ארץ ישראל וואו מען ניצט נישט MOISTURE CURE איז די מצב אסאך בעסער, איך מאך איהם נישט אוועק, JUST WONDERING
והוא פלאי האט געשריבן:
הייפער וויפיל יאר צוריק האט מען געפעינט אין די מערות אודאי זענען די. תתקע"ד דורות פון קדם בריאת העולם געוווען רשעים זיי האבן גענוצט כעין מויסטשער קיור
Megaloceros from Lascaux, France. In 2011, South African archeologists reported finding a 100,000-year-old human-made ochre-based mixture that could have been used like paint.[1]Cave paintings drawn with red or yellow ochre, hematite, manganese oxide, and charcoal may have been made by early Geder as long as 40,000 years ago.
אויף. דעם בין איך ארויפגעגאנגן! מעק עס נישט אויס, זאל יעדער זעהן די קראנטקייט פון דיינע מקורות. הרב הייפער
