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56-470: Polyols may be classified according to their chemistry. Some of these chemistries are polyether, polyester, polycarbonate and also acrylic polyols. Polyether polyols may be further subdivided and classified as polyethylene oxide or polyethylene glycol (PEG), polypropylene glycol (PPG) and Polytetrahydrofuran or PTMEG. These have 2, 3 and 4 carbons respectively per oxygen atom in the repeat unit. Polycaprolactone polyols are also commercially available. There

112-476: A carbonyl group C=O, which is a divalent group at C atom, which gives rise to 120° C–C–O and O–C–O angles. Unlike amides , carboxylic acid esters are structurally flexible functional groups because rotation about the C–O–C bonds has a low barrier. Their flexibility and low polarity is manifested in their physical properties; they tend to be less rigid (lower melting point) and more volatile (lower boiling point) than

168-444: A dehydrating agent: The equilibrium constant for such reactions is about 5 for typical esters, e.g., ethyl acetate. The reaction is slow in the absence of a catalyst. Sulfuric acid is a typical catalyst for this reaction. Many other acids are also used such as polymeric sulfonic acids . Since esterification is highly reversible, the yield of the ester can be improved using Le Chatelier's principle : Reagents are known that drive

224-401: A PEG structure to another larger molecule, for example, a therapeutic protein , which is then referred to as a PEGylated protein. PEGylated interferon alfa-2a or alfa-2b are commonly used injectable treatments for hepatitis C infection. PEG is soluble in water , methanol , ethanol , acetonitrile , benzene , and dichloromethane , and is insoluble in diethyl ether and hexane . It

280-619: A broad array of plastics , plasticizers , resins , and lacquers , and are one of the largest classes of synthetic lubricants on the commercial market. Polyesters are important plastics, with monomers linked by ester moieties . Esters of phosphoric acid form the backbone of DNA molecules. Esters of nitric acid , such as nitroglycerin , are known for their explosive properties. There are compounds in which an acidic hydrogen of acids mentioned in this article are not replaced by an organyl, but by some other group. According to some authors, those compounds are esters as well, especially when

336-597: A chain extender to further increase molecular weight though it does increase viscosity because more hydrogen bonding is introduced. Xylitol Sugar alcohols , a class of low molecular weight polyols, are commonly obtained by hydrogenation of sugars. They have the formula (CHOH) n H 2 , where n = 4–6. Sugar alcohols are added to foods because of their lower caloric content than sugars ; however, they are also, in general, less sweet, and are often combined with high-intensity sweeteners . They are also added to chewing gum because they are not broken down by bacteria in

392-955: A combination of hyperconjugation and dipole minimization effects. The preference for the Z conformation is influenced by the nature of the substituents and solvent, if present. Lactones with small rings are restricted to the s -trans (i.e. E ) conformation due to their cyclic structure. Esters derived from carboxylic acids and alcohols are more polar than ethers but less polar than alcohols. They participate in hydrogen bonds as hydrogen-bond acceptors, but cannot act as hydrogen-bond donors, unlike their parent alcohols. This ability to participate in hydrogen bonding confers some water-solubility. Because of their lack of hydrogen-bond-donating ability, esters do not self-associate. Consequently, esters are more volatile than carboxylic acids of similar molecular weight. Esters are generally identified by gas chromatography, taking advantage of their volatility. IR spectra for esters feature an intense sharp band in

448-407: A distribution of molecular weights (i.e. they are polydisperse). The size distribution can be characterized statistically by its weight average molecular weight ( M w ) and its number average molecular weight ( M n ), the ratio of which is called the polydispersity index ( Đ M ). M w and M n can be measured by mass spectrometry . PEGylation is the act of covalently coupling

504-680: A few hours. Polyethylene oxide, or high-molecular-weight polyethylene glycol, is synthesized by suspension polymerization . It is necessary to hold the growing polymer chain in solution in the course of the polycondensation process. The reaction is catalyzed by magnesium-, aluminium-, or calcium-organoelement compounds. To prevent coagulation of polymer chains from solution, chelating additives such as dimethylglyoxime are used. Alkaline catalysts such as sodium hydroxide (NaOH), potassium hydroxide (KOH), or sodium carbonate (Na 2 CO 3 ) are used to prepare low-molecular-weight polyethylene glycol. Ester group In chemistry , an ester

560-565: A part of metal and metalloid alkoxides , of which many hundreds are known, could be classified as esters of the corresponding acids (e.g. aluminium triethoxide ( Al(OCH 2 CH 3 ) 3 ) could be classified as an ester of aluminic acid which is aluminium hydroxide , tetraethyl orthosilicate ( Si(OCH 2 CH 3 ) 4 ) could be classified as an ester of orthosilicic acid , and titanium ethoxide ( Ti(OCH 2 CH 3 ) 4 ) could be classified as an ester of orthotitanic acid ). Esters derived from carboxylic acids and alcohols contain

616-450: A wide range of molecular weights from 300   g/mol to 10,000,000   g/mol. PEG and PEO are liquids or low-melting solids, depending on their molecular weights . While PEG and PEO with different molecular weights find use in different applications and have different physical properties (e.g. viscosity ) due to chain length effects, their chemical properties are nearly identical. Different forms of PEG are also available, depending on

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672-684: Is γ-valerolactone . An uncommon class of esters are the orthoesters . One of them are the esters of orthocarboxylic acids. Those esters have the formula RC(OR′) 3 , where R stands for any group (organic or inorganic) and R ′ stands for organyl group. For example, triethyl orthoformate ( HC(OCH 2 CH 3 ) 3 ) is derived, in terms of its name (but not its synthesis) from esterification of orthoformic acid ( HC(OH) 3 ) with ethanol . Esters can also be derived from inorganic acids. Inorganic acids that exist as tautomers form two or more types of esters. Some inorganic acids that are unstable or elusive form stable esters. In principle,

728-501: Is a compound derived from an acid (organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group ( −OH ) of that acid is replaced by an organyl group (R ′ ). These compounds contain a distinctive functional group . Analogues derived from oxygen replaced by other chalcogens belong to the ester category as well. According to some authors, organyl derivatives of acidic hydrogen of other acids are esters as well (e.g. amides ), but not according to

784-529: Is a dibutylstannylene ester of lauric acid , and the Phillips catalyst CrO 2 (OSi(OCH 3 ) 3 ) 2 is a trimethoxysilyl ester of chromic acid ( H 2 CrO 4 ). The word ester was coined in 1848 by a German chemist Leopold Gmelin , probably as a contraction of the German Essigäther , " acetic ether ". The names of esters that are formed from an alcohol and an acid, are derived from

840-492: Is a polyether compound derived from petroleum with many applications, from industrial manufacturing to medicine . PEG is also known as polyethylene oxide ( PEO ) or polyoxyethylene ( POE ), depending on its molecular weight . The structure of PEG is commonly expressed as H−(O−CH 2 −CH 2 ) n −OH. PEO's have "very low single dose oral toxicity", on the order of tens of grams per kilogram of human body weight when ingested by mouth. Because of its low toxicity, PEO

896-458: Is also an equilibrium process – essentially the reverse of the Fischer esterification reaction. Because an alcohol (which acts as the leaving group) and water (which acts as the nucleophile) have similar p K a values, the forward and reverse reactions compete with each other. As in transesterification, using a large excess of reactant (water) or removing one of the products (the alcohol) can promote

952-562: Is also an increasing trend to use biobased (and hence renewable) polyols. Polyether polyols have numerous uses. As an example, polyurethane foam is a big user of polyether polyols. Polyester polyols can be used to produce rigid foam. They are available in both aromatic and aliphatic versions. They are also available in mixed aliphatic-aromatic versions often made from recycled raw materials, typically polyethylene terephthalate (PET). Acrylic polyols are generally used in higher performance applications where stability to ultraviolet light

1008-540: Is also attributed to other molecules containing hydroxyl groups. For instance, polyvinyl alcohol is (CH 2 CHOH) n with n hydroxyl groups where n can be in the thousands. Cellulose is a polymer with many hydroxyl groups, but it is not referred to as a polyol. There are polyols based on renewable sources such as plant-based materials including castor oil and cottonseed oil . Vegetable oils and biomass are also potential renewable polyol raw materials. Seed oil can even be used to produce polyester polyols. Since

1064-648: Is considered too hazardous and expensive for large-scale applications. Carboxylic acids are esterified by treatment with epoxides , giving β-hydroxyesters: This reaction is employed in the production of vinyl ester resin from acrylic acid . Alcohols react with acyl chlorides and acid anhydrides to give esters: The reactions are irreversible simplifying work-up . Since acyl chlorides and acid anhydrides also react with water, anhydrous conditions are preferred. The analogous acylations of amines to give amides are less sensitive because amines are stronger nucleophiles and react more rapidly than does water. This method

1120-412: Is coupled to hydrophobic molecules to produce non-ionic surfactants . PEG and related polymers (PEG phospholipid constructs) are often sonicated when used in biomedical applications. However, as reported by Murali et al., PEG is very sensitive to sonolytic degradation and PEG degradation products can be toxic to mammalian cells. It is, thus, imperative to assess potential PEG degradation to ensure that

1176-413: Is difficult, the price for this type of quality is often 10–1000 fold that of polydisperse PEG. PEGs are also available with different geometries. The numbers that are often included in the names of PEGs indicate their average molecular weights (e.g. a PEG with n = 9 would have an average molecular weight of approximately 400 daltons , and would be labeled PEG 400 ). Most PEGs include molecules with

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1232-605: Is employed only for laboratory-scale procedures, as it is expensive. Trimethyloxonium tetrafluoroborate can be used for esterification of carboxylic acids under conditions where acid-catalyzed reactions are infeasible: Although rarely employed for esterifications, carboxylate salts (often generated in situ ) react with electrophilic alkylating agents , such as alkyl halides , to give esters. Anion availability can inhibit this reaction, which correspondingly benefits from phase transfer catalysts or such highly polar aprotic solvents as DMF . An additional iodide salt may, via

1288-603: Is one illustrative example. The carbonylation of methanol yields methyl formate , which is the main commercial source of formic acid . The reaction is catalyzed by sodium methoxide : In hydroesterification , alkenes and alkynes insert into the O−H bond of carboxylic acids. Vinyl acetate is produced industrially by the addition of acetic acid to acetylene in the presence of zinc acetate catalysts: Vinyl acetate can also be produced by palladium -catalyzed reaction of ethylene, acetic acid , and oxygen : Silicotungstic acid

1344-485: Is preferred in the biomedical field, whereas PEO is more prevalent in the field of polymer chemistry. Because different applications require different polymer chain lengths, PEG has tended to refer to oligomers and polymers with a molecular mass below 20,000   g/mol, PEO to polymers with a molecular mass above 20,000   g/mol, and POE to a polymer of any molecular mass. PEGs are prepared by polymerization of ethylene oxide and are commercially available over

1400-401: Is produced by the interaction of ethylene oxide with water, ethylene glycol , or ethylene glycol oligomers. The reaction is catalyzed by acidic or basic catalysts. Ethylene glycol and its oligomers are preferable as a starting material instead of water because they allow the creation of polymers with a low polydispersity (narrow molecular weight distribution). Polymer chain length depends on

1456-611: Is required and also lower VOC coatings. Other uses include direct to metal coatings. As they are used where good UV resistance is required, such as automotive coatings, the isocyanate component also tends to be UV resistant and hence isocyanate oligomers or prepolymers based on Isophorone diisocyanate are generally used. Caprolactone-based polyols produce polyurethanes with enhanced hydrolysis resistance. Polycarbonate polyols are more expensive than other polyols and are thus used in more demanding applications. They have been used to make an isophorone diisocyanate based prepolymer which

1512-464: Is the substitution reaction between a carboxylic acid ( R−C(=O)−OH ) and an alcohol ( R'−OH ), forming an ester ( R−C(=O)−O−R' ), where R stands for any group (typically hydrogen or organyl) and R ′ stands for organyl group. Organyl esters of carboxylic acids typically have a pleasant smell; those of low molecular weight are commonly used as fragrances and are found in essential oils and pheromones . They perform as high-grade solvents for

1568-478: Is then used in glass coatings. They may be used in reactive hotmelt adhesives . All polyols may be used to produce polyurethane prepolymers . These then find use in coatings , adhesives , sealants and elastomers . Low molecular weight polyols are widely used in polymer chemistry where they function as crosslinking agents and chain extenders. Alkyd resins for example, use polyols in their synthesis and are used in paints and in molds for casting . They are

1624-499: Is used as an acyl-transfer catalyst . Another method for the dehydration of mixtures of alcohols and carboxylic acids is the Mitsunobu reaction : Carboxylic acids can be esterified using diazomethane : Using this diazomethane, mixtures of carboxylic acids can be converted to their methyl esters in near quantitative yields, e.g., for analysis by gas chromatography . The method is useful in specialized organic synthetic operations but

1680-476: Is used in a variety of edible products. It is also used as a lubricating coating for various surfaces in aqueous and non-aqueous applications. The precursor to PEGs is ethylene oxide , which is hazardous. Ethylene glycol and its ethers are nephrotoxic ( poisonous to the kidneys ) if applied to damaged skin. The United States Food and Drug Administration (FDA or US FDA) regards PEG as biologically inert and safe. A 2015 study appears to challenge

1736-495: Is used in the production of ethyl acetate from acetaldehyde . Esters are less reactive than acid halides and anhydrides. As with more reactive acyl derivatives, they can react with ammonia and primary and secondary amines to give amides, although this type of reaction is not often used, since acid halides give better yields. Esters can be converted to other esters in a process known as transesterification . Transesterification can be either acid- or base-catalyzed, and involves

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1792-411: Is used to manufacture ethyl acetate by the alkylation of acetic acid by ethylene: The Tishchenko reaction involves disproportionation of an aldehyde in the presence of an anhydrous base to give an ester. Catalysts are aluminium alkoxides or sodium alkoxides. Benzaldehyde reacts with sodium benzyloxide (generated from sodium and benzyl alcohol ) to generate benzyl benzoate . The method

1848-500: The Finkelstein reaction , catalyze the reaction of a recalcitrant alkyl halide. Alternatively, salts of a coordinating metal, such as silver, may improve the reaction rate by easing halide elimination. Transesterification , which involves changing one ester into another one, is widely practiced: Like the hydrolysation, transesterification is catalysed by acids and bases. The reaction is widely used for degrading triglycerides , e.g. in

1904-766: The IUPAC . Glycerides are fatty acid esters of glycerol ; they are important in biology, being one of the main classes of lipids and comprising the bulk of animal fats and vegetable oils . Lactones are cyclic carboxylic esters; naturally occurring lactones are mainly 5- and 6-membered ring lactones. Lactones contribute to the aroma of fruits, butter, cheese, vegetables like celery and other foods. Esters can be formed from oxoacids (e.g. esters of acetic acid , carbonic acid , sulfuric acid , phosphoric acid , nitric acid , xanthic acid ), but also from acids that do not contain oxygen (e.g. esters of thiocyanic acid and trithiocarbonic acid ). An example of an ester formation

1960-481: The initiator used for the polymerization process – the most common initiator is a monofunctional methyl ether PEG, or methoxypoly(ethylene glycol), abbreviated mPEG. Lower-molecular-weight PEGs are also available as purer oligomers, referred to as monodisperse, uniform, or discrete. Very high-purity PEG has recently been shown to be crystalline, allowing the determination of a crystal structure by x-ray crystallography . Since purification and separation of pure oligomers

2016-573: The organyl parts of the carboxylic acid and the alcohol, respectively, and R can be a hydrogen in the case of esters of formic acid . For example, butyl acetate (systematically butyl ethanoate), derived from butanol and acetic acid (systematically ethanoic acid) would be written CH 3 CO 2 (CH 2 ) 3 CH 3 . Alternative presentations are common including BuOAc and CH 3 COO(CH 2 ) 3 CH 3 . Cyclic esters are called lactones , regardless of whether they are derived from an organic or inorganic acid. One example of an organic lactone

2072-400: The reaction product . Esters are common in organic chemistry and biological materials, and often have a pleasant characteristic, fruity odor. This leads to their extensive use in the fragrance and flavor industry. Ester bonds are also found in many polymers . The classic synthesis is the Fischer esterification , which involves treating a carboxylic acid with an alcohol in the presence of

2128-459: The FDA's conclusion. In the study, a high-sensitivity ELISA assay detected anti-PEG antibodies in 72% of random blood plasma samples collected from 1990 to 1999. According to the study's authors, this result suggests that anti-PEG antibodies may be present, typically at low levels, in people who were never treated with PEGylated drugs. Due to its ubiquity in many products and the large percentage of

2184-427: The aroma of many fruits, including apples , durians , pears , bananas , pineapples , and strawberries . Several billion kilograms of polyesters are produced industrially annually, important products being polyethylene terephthalate , acrylate esters , and cellulose acetate . Esterification is the general name for a chemical reaction in which two reactants (typically an alcohol and an acid) form an ester as

2240-420: The corresponding amides . The p K a of the alpha-hydrogens on esters of carboxylic acids is around 25 (alpha-hydrogen is a hydrogen bound to the carbon adjacent to the carbonyl group (C=O) of carboxylate esters). Many carboxylic acid esters have the potential for conformational isomerism , but they tend to adopt an S - cis (or Z ) conformation rather than the S - trans (or E ) alternative, due to

2296-460: The dehydration of mixtures of alcohols and carboxylic acids. One example is the Steglich esterification , which is a method of forming esters under mild conditions. The method is popular in peptide synthesis , where the substrates are sensitive to harsh conditions like high heat. DCC ( dicyclohexylcarbodiimide ) is used to activate the carboxylic acid to further reaction. 4-Dimethylaminopyridine (DMAP)

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2352-444: The dominant resin or "binder" in most commercial "oil-based" coatings. Approximately 200,000 tons of alkyd resins are produced each year. They are based on linking reactive monomers through ester formation. Polyols used in the production of commercial alkyd resins are glycerol , trimethylolpropane , and pentaerythritol . In polyurethane prepolymer production, a low molecular weight polyol- diol such as 1,4-butanediol may be used as

2408-416: The final material does not contain undocumented contaminants that can introduce artifacts into experimental results. PEGs and methoxypolyethylene glycols are manufactured by Dow Chemical under the trade name Carbowax for industrial use, and Carbowax Sentry for food and pharmaceutical use. They vary in consistency from liquid to solid, depending on the molecular weight, as indicated by a number following

2464-408: The first carbon atom of the organyl group replacing acidic hydrogen, is replaced by another atom from the group 14 elements ( Si , Ge , Sn , Pb ); for example, according to them, trimethylstannyl acetate (or trimethyltin acetate) CH 3 COOSn(CH 3 ) 3 is a trimethylstannyl ester of acetic acid , and dibutyltin dilaurate (CH 3 (CH 2 ) 10 COO) 2 Sn((CH 2 ) 3 CH 3 ) 2

2520-495: The forward reaction. Basic hydrolysis of esters, known as saponification , is not an equilibrium process; a full equivalent of base is consumed in the reaction, which produces one equivalent of alcohol and one equivalent of a carboxylate salt. The saponification of esters of fatty acids is an industrially important process, used in the production of soap. Esterification is a reversible reaction. Esters undergo hydrolysis under acidic and basic conditions. Under acidic conditions,

2576-438: The generic term polyol is only derived from chemical nomenclature and just indicates the presence of several hydroxyl groups, no common properties can be assigned to all polyols. However, polyols are usually viscous at room temperature due to hydrogen bonding. Polyethylene oxide Polyethylene glycol ( PEG ; / ˌ p ɒ l i ˈ ɛ θ əl ˌ iː n ˈ ɡ l aɪ ˌ k ɒ l , - ˈ ɛ θ ɪ l -, - ˌ k ɔː l / )

2632-839: The mouth or metabolized to acids, and thus do not contribute to tooth decay . Maltitol , sorbitol , xylitol , erythritol , and isomalt are common sugar alcohols. Polyether polyol (The oxygen atoms of the ether linkages are shown in blue.) (The oxygen and carbon atoms of the ester groups are shown in blue.) The term polyol is used for various chemistries of the molecular backbone. Polyols may be reacted with diisocyanates or polyisocyanates to produce polyurethanes . MDI finds considerable use in PU foam production. Polyurethanes are used to make flexible foam for mattresses and seating, rigid foam insulation for refrigerators and freezers , elastomeric shoe soles, fibers (e.g. Spandex ), coatings, sealants and adhesives . The term polyol

2688-521: The name. They are used commercially in numerous applications, including foods, cosmetics , pharmaceutics, biomedicine , dispersing agents, solvents, ointments , suppository bases, as tablet excipients , and as laxatives . Some specific groups are lauromacrogols , nonoxynols , octoxynols , and poloxamers . The production of polyethylene glycol was first reported in 1859. Both A. V. Lourenço and Charles Adolphe Wurtz independently isolated products that were polyethylene glycols. Polyethylene glycol

2744-448: The other hand, more frequently named using the systematic IUPAC name, based on the name for the acid followed by the suffix -oate . For example, the ester hexyl octanoate, also known under the trivial name hexyl caprylate , has the formula CH 3 (CH 2 ) 6 CO 2 (CH 2 ) 5 CH 3 . The chemical formulas of organic esters formed from carboxylic acids and alcohols usually take the form RCO 2 R' or RCOOR', where R and R' are

2800-464: The parent alcohol and the parent acid, where the latter may be organic or inorganic. Esters derived from the simplest carboxylic acids are commonly named according to the more traditional, so-called " trivial names " e.g. as formate, acetate, propionate, and butyrate, as opposed to the IUPAC nomenclature methanoate, ethanoate, propanoate, and butanoate. Esters derived from more complex carboxylic acids are, on

2856-530: The population with antibodies to PEG, which indicates an allergic reaction, hypersensitive reactions to PEG are an increasing health concern. Allergy to PEG is usually discovered after a person has been diagnosed with an allergy to several seemingly unrelated products—including processed foods, cosmetics, drugs, and other substances—that contain or were manufactured with PEG. PEG , PEO , and POE refer to an oligomer or polymer of ethylene oxide . The three names are chemically synonymous, but historically PEG

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2912-467: The production of fatty acid esters and alcohols. Poly(ethylene terephthalate) is produced by the transesterification of dimethyl terephthalate and ethylene glycol: A subset of transesterification is the alcoholysis of diketene . This reaction affords 2-ketoesters. Alkenes undergo carboalkoxylation in the presence of metal carbonyl catalysts. Esters of propanoic acid are produced commercially by this method: A preparation of methyl propionate

2968-440: The range 1730–1750 cm assigned to ν C=O . This peak changes depending on the functional groups attached to the carbonyl. For example, a benzene ring or double bond in conjunction with the carbonyl will bring the wavenumber down about 30 cm . Esters are widespread in nature and are widely used in industry. In nature, fats are, in general, triesters derived from glycerol and fatty acids . Esters are responsible for

3024-488: The ratio of reactants. Depending on the catalyst type, the mechanism of polymerization can be cationic or anionic. The anionic mechanism is preferable because it allows one to obtain PEG with a low polydispersity . Polymerization of ethylene oxide is an exothermic process. Overheating or contaminating ethylene oxide with catalysts such as alkalis or metal oxides can lead to runaway polymerization, which can end in an explosion after

3080-406: The reaction is the reverse reaction of the Fischer esterification . Under basic conditions, hydroxide acts as a nucleophile, while an alkoxide is the leaving group. This reaction, saponification , is the basis of soap making. The alkoxide group may also be displaced by stronger nucleophiles such as ammonia or primary or secondary amines to give amides (ammonolysis reaction): This reaction

3136-420: The reaction of an ester with an alcohol. Unfortunately, because the leaving group is also an alcohol, the forward and reverse reactions will often occur at similar rates. Using a large excess of the reactant alcohol or removing the leaving group alcohol (e.g. via distillation ) will drive the forward reaction towards completion, in accordance with Le Chatelier's principle . Acid-catalyzed hydrolysis of esters

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