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The Street Chemist - Part 14

The final flammable-liquid hydrocarbon derivative family is ester. In addition to being flammable, esters may polymerize.Esters

The final flammable-liquid hydrocarbon derivative family is ester. In addition to being flammable, esters may polymerize. They have moderate boiling and flash points, narrow flammable ranges, and high ignition temperatures. Esters are made through a process referred to as esterification. An ester is formed when an alcohol is combined with an organic acid with water as a by-product. This process is illustrated in the following example by combining acrylic acid and methyl alcohol; the resulting ester compound is methyl acrylate.

Esters have a carbon double bonded to one oxygen atom and a single bond with another oxygen. Esters are carbonyls and are polar. The degree of polarity is much less than organic acids and alcohols and is similar to ketones and aldehydes. Esters are miscible in water and require polar-solvent foams when fighting fires.

In this book, only three esters will be discussed because of their common commercial use. The general formula for ester is R-C-O-O-R, or R-C-O2-R. There are two radicals in the ester compounds. Because nothing is ever called ester, the word ester will not appear in the name of the compound. The radical that is attached to the carbon in the functional group determines which ester compound it will be.

Esters are one of the functional groups in which all the carbons are counted, including the carbon in the functional group when naming the type of ester compound. In addition, esters use the alternate name for one- and two-carbon radicals that are attached to the carbon in the functional group only. The radical on the other side is named in the normal way. The ester is named with the radical on the right first, ending in the name of the type of ester on the left. Certain radicals attached to the carbon of the functional group will produce certain esters. For example, in a one-carbon ester the carbon in the functional group is used as the one carbon. A single hydrogen atom is attached to the carbon in the functional group to complete the bonding requirements.

A one-carbon ester uses the alternate name for one carbon, which is "form"; esters end in "ate", so the name of a one-carbon ester is formate. Any radical can be attached to the oxygen in the functional group. If a methyl were added to the oxygen, the name of the ester compound is methyl formate. When a methyl radical is attached to the carbon in the functional group, it forms a two-carbon chain. The alternate name for two carbons, "acet", is used; the ending "ate" is used to indicate an ester, so a two-carbon ester is an acetate. The second radical added to the oxygen in the functional group determines what type of acetate the compound is. Theoretically, any radical can be used. If a vinyl radical were used, the compound would be vinyl acetate.

The last ester has a vinyl radical attached to the carbon in the functional group. This forms a three-carbon chain with one double bond in the chain. The name for a three-carbon radical with one double bond is "acryl". The ending for the ester is "ate"; so the ester is called acrylate. Any radical can be attached to the oxygen in the functional group. If a methyl is attached, the ester compound is called methyl acrylate. In the following illustrations, the structures and molecular formulas are shown for methyl formate, vinyl acetate, and methyl acrylate. There can be other radicals attached to the oxygen, which change the name of the compound.

Methyl formate is a colorless liquid with an agreeable odor. It is a dangerous fire and explosion risk, with a flammable range of 5 to 23% in air. The boiling point is 89

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