Esters

Submitted by ChemPRIME Staff on Thu, 12/16/2010 - 13:09


Cellulose acetate is a complicated example of another groupThose elements that comprise a single column of the periodic table. Also called family. of organicRefers to the branch of chemistry that studies compounds containing carbon, usually in combination with hydrogen and other elements such as O, N, S, and P. Certain small ions and compounds containing carbon (such as carbonate ions and carbon dioxide) are not considered to be organic, but rather are classed as inorganic. compounds, esters, which can be made by combining alcohols with acids. A simpler case is the reaction of ethanol with acetic acid to give ethyl acetate:


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The general formula for an ester can be written .

In the case of ethyl acetate, R is CH3CH2 and R′ is CH3. When this notation is used, esters are named based on the number of carbon atomsThe smallest particle of an element that can be involved in chemical combination with another element; an atom consists of protons and neutrons in a tiny, very dense nucleus, surrounded by electrons, which occupy most of its volume. present in the alcohol and carboxylic acid groups that helped to form it. The term from the alcohol is given the "-yl" suffix, and is followed by the acid term with the suffix "-ate". As an example, the ester formed by the condensation reactionA chemical reaction in which two molecules combine to form a very small molecule and a larger molecule than either of the two reactants. An example is formation of an ester from a carboxylic acid and an alcohol. between methanol and butanoic acid would be called "methyl butanoate".

The synthesisFormation of substances with more complicated sturctures than do their precursors. of nitroglycerin, was also an example of ester formation, but in that case an inorganicPertaining to the chemistry of elements other than carbon and compounds containing at most a small amount of carbon. acid, HNO3, was combined with an alcohol.

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Formation of an ester is an example of an important class of reactions called condensations. In a condensation reaction a pair of molecules join together, giving off a small, very stable molecule like H2O or HCl. In both ethyl acetate and nitroglycerin synthesis, this small molecule is H2O. A condensation can often be undone if large numbers of the small molecules are added to the productA substance produced by a chemical reaction.. In the case of an ester, addition of large quantities of H2O causes hydrolysisAny reaction in which water (hydro) is split into two parts (lysis). Examples include the reaction of an anion with water to form the conjugate acid and hydroxide ion and hydrolysis of an ester or amide, in which the H from water bonds to form an alcohol or amine and the OH bonds to a carbonyl carbon to form a carboxylic acid. (literally, “splitting by means of water“):


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This is just the reverse of ethyl acetate condensation.

Although the ester functional group has a polarDescribes a molecule that has separated, equal positive and negative charges that consitute a positive and a negative pole; such a molecule tends to assume certain orientations more than others in an electric field. carbonylThe functional group consisting of a carbon atom doubly bonded to an oxygen atom; found in aldehydes and ketones., it contains no hydrogen atoms suitable for hydrogen bonding. Therefore esters have low boiling points relative to most molecules of similar size. In many cases, even though its molecules are almost twice as large as those of the constituent alcohol and acid, an ester is found to have a lower boiling point than either. Ethyl acetate, for example, boils at 77.1°C, lower than ethanol (78.5°C) or acetic acid (117.9°C). By contrast to acids and alcohols which have unpleasant and rather weak odors, respectively, esters usually smell good. The odors of many fruits and flowers are due to esters. Ethyl acetate, for example, is the most important factor in the flavor of pineapples.