Chemical compound
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Acrylic acid (IUPAC: prop-2-enoic acid) is an organic compound with the formula CH2=CHCOOH. It is the simplest unsaturated carboxylic acid, consisting of a vinyl group connected directly to a carboxylic acid terminus. This colorless liquid has a characteristic acrid or tart smell. It is miscible with water, alcohols, ethers, and chloroform. More than a million tons are produced annually.[7]
History
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The word "acrylic" was coined in , for a chemical derivative of acrolein, an acrid-smelling oil derived from glycerol.
Production
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Acrylic acid is produced by oxidation of propylene, which is a byproduct of the production of ethylene and gasoline:
- 2 CH2=CHCH3 + 3 O2 &#; 2 CH2=CHCO2H + 2 H2O
Historical methods
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Because acrylic acid and its esters have long been valued commercially, many other methods have been developed. Most have been abandoned for economic or environmental reasons. An early method was the hydrocarboxylation of acetylene ("Reppe chemistry"):
This method requires nickel carbonyl, high pressures of carbon monoxide, and acetylene, which is relatively expensive compared to propylene.
Acrylic acid was once manufactured by the hydrolysis of acrylonitrile, a material derived from propene by ammoxidation, but this route was abandoned because it cogenerates ammonium side products, which must be disposed of. Other now abandoned precursors to acrylic acid include ethenone and ethylene cyanohydrin.[7]
Research
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Carboxylating ethylene to acrylic acid under supercritical carbon dioxide is thermodynamically possible, but efficient catalysts have not been developed.[8] 3-Hydroxypropionic acid (3HP), an acrylic-acid precursor by dehydration, can be produced from sugars, but the process is not competitive.[9][10]
Reactions and uses
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Acrylic acid undergoes the typical reactions of a carboxylic acid. When reacted with an alcohol, it forms the corresponding ester. The esters and salts of acrylic acid are collectively known as acrylates (or propenoates). The most common alkyl esters of acrylic acid are methyl, butyl, ethyl, and 2-ethylhexyl acrylate.
Acrylic acid and its esters readily combine with themselves (to form polyacrylic acid) or other monomers (e.g. acrylamides, acrylonitrile, vinyl compounds, styrene, and butadiene) by reacting at their double bond, forming homopolymers or copolymers, which are used in the manufacture of various plastics, coatings, adhesives, elastomers, as well as floor polishes and paints.
Acrylic acid is used in many industries, including the diaper industry, the water treatment industry, and the textile industry. The annual worldwide consumption of acrylic acid is projected to reach more than an estimated 8,000 kilotons by . This increase is expected due to its use in new applications, including personal care products, detergents, and products for adult incontinence.[11]
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Substituents
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As a substituent acrylic acid can be found as an acyl group or a carboxyalkyl group, depending on the removal of the group from the molecule.
More specifically, these are:
- The acryloyl group, with the removal of the &#;OH from carbon-1.
- The 2-carboxyethenyl group, with the removal of a &#;H from carbon-3. This substituent group is found in chlorophyll.
Safety
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Acrylic acid is severely irritating and corrosive to the skin and the respiratory tract. Eye contact can result in severe and irreversible injury. Low exposure will cause minimal or no health effects, while high exposure could result in pulmonary edema. The LD50 is 340 mg/kg (rat, oral) with the lowest recorded LD50 being 293 mg/kg (oral, rat) comparable to ethylene glycol which is indicative of being a potent poison.[12] Ethyl acrylate was once used as synthetic food flavoring and was withdrawn by FDA possibly due to cancerogenic effects observed in lab animals.[13]
Animal studies showed that high-doses of acrylic acid decreased weight gain. Acrylic acid can be converted to non-toxic lactic acid.[14]
Acrylic acid is a constituent of tobacco smoke.[15]
See also
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References
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What Are Acrylic Polymers and How Are They Used?
Acrylic polymer emulsions are one of the great success stories of modern industrial chemistry. The science behind this versatile class of polymers was perfected just after World War II, driven by an unprecedented housing boom and the demand for more versatile, more efficient paints. The result was household acrylic paint, an aqueous technology that required less preparation to use, was easier to clean up, had less odor, and performed better than paints made with solvents.
Today, acrylic acid remains an essential building block in the production of some of our most commonly used industrial and consumer products. Approximately two-thirds of the U.S. supply of acrylic acid is used to produce the acrylic esters methyl acrylate, butyl acrylate, ethyl acrylate, and 2-ethylhexyl acrylate. Taken together, acrylic acid and its esters are known as acrylates, and they are used as ingredients in a wide variety of products, including paints, coatings, textiles, adhesives and plastics.
The versatility of acrylic polymers is made possible by the number of building blocks available for polymer synthesis, as well as diverse ester functionality. Chemists select appropriate hard and soft monomers in order to build acrylic polymers with specific attributes for a variety of end-use applications. Pure acrylic polymers are also possible, resulting in polyacrylic acid or crosslinked polyacrylic acid compounds, which are used in the manufacture of hygienic products, detergents, and water purification and wastewater treatment.
Household Paints and Beyond
As previously discussed, acrylic resins offer a significant advantage as ingredients in latex paint. They provide greater resistance to blistering and cracking, are extremely waterproof and can last for decades without yellowing when exposed to UV light. As chemists tweak their formulas, they can increase the desirable properties of the paint. Today&#;s latex paints often deliver enhanced dirt pick-up resistance, superior gloss and excellent color retention, all while providing long-lasting wood protection against the effects of weathering damage.
But acrylic polymers have a number of other practical applications beyond paints. Acrylic polymers are commonly used in pressure-sensitive adhesives (PSAs), which rely on subtle pressure to create a bond. Applying this pressure enables the adhesive to &#;wet out&#; &#; to flow and cover a substrate to maximize the contact area and the attractive forces between the adhesive and bonding surface. For an adhesive to effectively wet out a surface, the surface energy of the adhesive must be as low or lower than the surface energy of the substrate to be bonded. In addition to surface energy, the usual tack, peel and shear properties must also be considered. PSAs are found in a number of applications, from shipping labels to foam insulating tape to laminating adhesives.
The construction industry has also found great success modifying Portland cement with acrylic-based polymers. The polymers improve several functional attributes of the cement, including adhesion to the old surface, flexural strength, tensile strength, and freeze/thaw durability. They also reduce permeability, halt the intrusion of chlorides and increase abrasion resistance. Acrylics and styrene-acrylics as well as styrene-butadiene polymers are used in applications involving cement.
Finally, acrylic emulsion polymers products are important components for graphic arts and barrier coatings applications. Acrylic emulsion polymers are readily formulated into overprint varnishes and inks to impart water resistance, rub resistance, alkaline resistance, and high gloss. They also can be incorporated into barrier coatings for paper and paperboard products, improving oil, grease and water resistance.
Partner with Us
Mallard Creek Polymers can work with you to find an existing acrylic polymer that fits your end use &#; or develop a new one. Check out our Guide to Tailoring an Emulsion Polymer Recipe or contact us today to discuss what we can make for you.