ester

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ester,

any one of a group of organic compounds with general formula RCO2R′ (where R and R′ are alkyl groups or aryl groups) that are formed by the reaction between an alcohol and an acid. For example, when ethanol and acetic acid react, ethyl acetate (an ester) and water are formed; the reaction is called esterification. Ethyl acetateacetate
, one of the most important forms of artificial cellulose-based fibers; the ester of acetic acid. The first patents for the production of fibers from cellulose acetate appeared at the beginning of the 20th cent.
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 is used as a solvent. Methyl acetate, formed by the reaction between methanol and acetic acid, is a sweet-smelling liquid used in making perfumes, extracts, and lacquers. Esters react with water (hydrolysishydrolysis
, chemical reaction of a compound with water, usually resulting in the formation of one or more new compounds. The most common hydrolysis occurs when a salt of a weak acid or weak base (or both) is dissolved in water.
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) under basic conditions to form an alcohol and an acid. When heated with a hydroxide certain esters decompose to yield soap and glycerin; the process is called saponification. Common fats and oilsfats and oils,
group of organic substances that form an important part of the diet and also are useful in many industries. The fats are usually solid, the oils generally liquid at ordinary room temperatures.
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 are mixtures of various esters, such as stearinstearin
, fat that is the triglyceride of stearic acid, CH3(CH2)16CO2H, i.e., the tristearate ester of glycerol. It is a white crystalline solid at ordinary temperatures and is insoluble in water and very slightly soluble in alcohol.
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, palmitinpalmitin
, fat that is the triglyceride of palmitic acid, CH3(CH2)14CO2H, i.e., the tripalmitate ester of glycerol. It is a white crystalline solid at ordinary temperatures, insoluble in water but soluble in ethanol and ether.
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, and linolein, formed from the alcohol glycerolglycerol,
 glycerin,
 glycerine,
or 1,2,3-propanetriol
, CH2OHCHOHCH2OH, colorless, odorless, sweet-tasting, syrupy liquid. Glycerol is a trihydric alcohol. It melts at 17.
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 and fatty acidsfatty acid,
any of the organic carboxylic acids present in fats and oils as esters of glycerol. Molecular weights of fatty acids vary over a wide range. The carbon skeleton of any fatty acid is unbranched. Some fatty acids are saturated, i.e.
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. Naturally occurring esters of organic acids in fruits and flowers give them their distinctive odors. Esters perform important functions in the animal body; e.g., the ester acetylcholine is a chemical transmitter of nerve stimuli.

Ester

 

any of a number of organic compounds, such as C2H5OCOCH3 or C5H11ONO, that are derived from acids by replacing the hydroxyl group (OH) with an alcohol, enol, or phenol radical (OR).

Esters are structural analogues of the salts of oxygen acids, but where a metal atom would be attached to the salt, a hydrocarbon group (R) is attached to the ester. The nomenclature for the salts and esters is similar; for example, NaOCOCH3 is called sodium acetate, and C2H5OCOCH3 is known as ethyl acetate. Like salts, esters form products of incomplete and complete replacement with dibasic and multibasic acids; thus, there are acid esters, such as monomethylsulfate (HOSO2OCH3), and complete (neutral) esters, such as dimethylsulfate (CH3OSO2OCH3).

Esters differ greatly from salts in their properties, however. Typical organic compounds, esters are usually volatile liquids. In some instances, they have a fruity or flowery fragrance. Virtually insoluble in water, they are readily soluble in organic solvents. Esters are hydrolyzed by the action of water to form the corresponding alcohol and acid, in accordance with the general formula

RCOOR′ + H2O ⇆ RCOOH + HOR′

The reaction is catalyzed by acids and even more so by bases. When alkaline catalysts are used, salts of acids are formed instead of free acids; the reaction is irreversible. Of the other reactions in which esters display acylating properties, the most common are transesterification, alcoholysis, and double exchange reactions. Some esters—for example, those formed by the lower aliphatic alcohols and such acids as sulfuric, trifluoroacetic, phosphoric, and phthalic acids—also have alkylating properties (seeDIMETHYL SULFATE and ).

Esters are usually obtained by esterification (see). They may also be formed by the acylation of alcohols by various acid derivatives (including acid halides and anhydrides), by the action of acid salts on alkyl halides, as in the reaction

C2H5I + AgONO → C2H5ONO + AgI

or by the action of acids on olefins, as in the reaction

HOSO2OH + CH2=CH2 → HOSO2OCH2CH3

Esters of glycerin and the higher carboxylic acids are the principal components of fats, and esters of the higher monohydric aliphatic alcohols and carboxylic acids are the main components of waxes. Other esters—mainly those of the terpene alcohols—are components of essential oils. Esters are used in technology as plastic monomers (acrylates and vinyl acetates), plasticizers for plastics (dioctyl and dibutyl phthalates), detergents (alkyl sulfates), solvents (amyl, butyl, and ethyl acetates), extraction agents and pesticides (esters of phosphoric acid), explosives (esters of nitric acid and polyhydric alcohols, such as nitroglycerin), pharmaceuticals (validol and aspirin), and fragrances (benzyl acetate and terpenyl acetate). Many esters of high molecular weight (including polyethylene terephthalate and cellulose acetates) are used in industry as plastics, lacquers, and synthetic fibers (seeALKYD RESINS and POLYESTER FIBER).

REFERENCES

Nesmeianov, A. N., and N. A. Nesmeianov. Nachala organicheskoi khimii, books 1–2. Moscow, 1969–70.
Chichibabin, A. E. Osnovnye nachala organicheskoi khimii, 7th ed., vol. 1. Moscow, 1963.

ester

[′es·tər]
(organic chemistry)
The compound formed by the elimination of water and the bonding of an alcohol and an organic acid.

ester

Chem any of a class of compounds produced by reaction between acids and alcohols with the elimination of water. Esters with low molecular weights, such as ethyl acetate, are usually volatile fragrant liquids; fats are solid esters
References in periodicals archive ?
We also found that SC components were not fully acquired like adults, determined by a lower ceramide level, contents of sebum with an ester bond at each site, and the higher protein secondary structure (ratio of [beta]/[alpha]) at the buttocks and inner upper arms.
Furthermore, the introduction of the thioester bond between the spacer and the biphenyl mesogen induced a lowering of transition temperatures in comparison with the polyester having ester bonds between the spacer and the biphenyl mesogen.
The reactions are formally of the second order; however, since in this study the number of monomer molecules added to one polyester macromolecule ([r.sub.0] = [R][.sub.0]/[P][.sub.0]) was always [less than or equal to]1 and was further reduced to r < [r.sub.0] because of the monomer lost by evaporation/sublimation, the concentration of the inner ester bonds was certainly much higher than [A][.sub.0] and, therefore, it can be assumed that [B] is in fact a constant equal to [B][.sub.0].
Ester bond Retention in tensile strength (%) Description concentration (a) 1 week 2 weeks 3 weeks PTMO-1U 0.4 64 (b) (b) PTMO-2U 0.4 23 (b) (b) PHMOU 0.25 124 106 45 PHMOCU-1 90 93 87 PHMOCU-2 78 54 36 PHMOCU-3 34 20 12 PHMCU 107 105 114 PCLU 0.16 104 101 104 PEAU 0.25 98 100 101 PBAU 0.20 99 100 101 Retention in ultimate elongation (%) Description 1 week 2 weeks 3 weeks PTMO-1U 3 (b) (b) PTMO-2U 103 (b) (b) PHMOU 144 106 0.1 PHMOCU-1 95 95 95 PHMOCU-2 104 104 96 PHMOCU-3 100 83 102 PHMCU 102 99 104 PCLU 101 100 102 PEAU 104 110 102 PBAU 99 102 99 (a) The number of ester bonds/the number of carbon atoms in a main chain per a polyester repetitive unit.
The factors which have effect on the polymer reactivity and thereby hydrolysis of polymer, are diffusion rate of water and degradation products that change the auto-acceleration of hydrolysis in ester bonds.
In this study, the biodegradable HMW star copolymers with Mw above the renal threshold are composed of pHPMA precursors with [M.sub.w] of approximately 27 000 g/mol coupled via amide bonds to a bis-MPA core containing hydrolytically degradable ester bonds. The stability of the HMW polymers was tested by incubation in phosphate buffer (pH 5.0 and pH 7.4), mimicking either the pH of the hypoxic environment of tumors and tumor cells (5.0) or the physiological pH of normoxic body tissue (7.4).
Such improvement is due to the formation of ester bonds between anhydride groups of coupling agents entered into an esterification reaction with the surface hydroxyl groups of wood fibers [8, 9].
Bacteria and fungi secrete PHBdepolymerase (EC 3.1.1.75), which hydrolyses the ester bonds of PHB and produces oligomers and/or monomer of 3hydroxybutyrate.
Biocatalysts carried out various trials and finally came up with the enzyme Pectinase 872L which works by catalysing the hydrolysis of the methyl ester bonds in pectin, releasing free carboxyl groups.
"My calculations suggested there was just enough phosphate to explain the amount of growth they saw." Others joined in the fray, pointing out that the arsenate ester bonds that would be required to make arsenic-based DNA are unstable in water, with an estimated half-life of less than one second.
has been granted a patent for a starch-based coating composition comprised of a naturally derived resin and a resin composition obtained by reacting a starch and/or a starch that has been esterified, etherified, oxidized, acid treated or dextrinated or modified by comprising one or more groups selected from the group consisting of aliphatic saturated hydrocarbon groups, aliphatic unsaturated hydrocarbon groups, and aromatic hydrocarbon groups, which are bonded by ester bonds and/or ether bonds to the starch or to a decomposition product of a starch that has been processed by a low molecularization treatment with an enzyme, acid or oxidizing agent, with a compound containing an isocyanate group obtained by reacting a polyisocyanate compound and a polyhydric alcohol.
The hydrolase enzymes selectively catalyze the formation of the amide or ester bonds between carboxylic acid, ester, or amide functional groups and the alcohol groups of the organosilicon reactant.