Aliphatic dicarboxylic acid esters

Ester spices synthesized from carboxylic acids and alcohols are a very important category of spices. According to the raw materials used in the synthesis, they are roughly divided into: aliphatic carboxylic esters, unsaturation carboxylic esters such as containing alkene and alkyne, aromatic carboxylic esters and other esters. One characteristic of ester spices is that carboxylic esters can be considered as the product of carboxylic acid after its hydroxyl groups are replaced by alkoxy groups. Because hydroxyl groups can be substituted with one or more kinds of alkoxy groups, the product can be monoester, diester or multiesters. Furthermore, an alcohol can also have several hydroxyl groups, which can react with one or more kinds of carboxyls to form a monocarboxylic ester or a multicarboxylic ester. The aroma and its type, intensity and characteristics are related to the structure of esters. An ester product of a lower carboxylic acid and a lower alcohol is generally a volatile liquid, with the aroma of flower, fruit and grass. An ester product of a lower carboxylic acid and a lower terpene alcohol has a flower aroma. Most esters with aryl groups have flower aroma. Ester products of aromatic carboxylic acids and aromatic alcohols generally have a not strong but lasting aroma with a higher boiling point. The widely existed ester spices can be found in the roots, stems, leaves, fruits, seeds, bark, flowers and other parts of plants and also found in some animal secretions. More ester spices are artificially synthesized. Synthetic esters are widely used for their easy synthetic procedures, wide source of raw materials, wide range of flavors and lower cost.

Aliphatic compounds, also known as open-chain compounds belong to one of the basic types of organic compounds. Carbon atoms of these compounds form a chain structure in their molecules. According to the structure and nature of the open-chain they can be divided into saturated and unsaturated aliphatic hydrocarbons. The former only have single bonds between carbon atoms, such as ethane and ethanol; the others such as ethylene and acetylene, have double and triple bonds between carbon atoms. Paraffinic hydrocarbons, alkenes and alkynes and their derivatives all belong to such compounds. Carbon chain structure without branches is called unbranched chain and the branch part is called side chain. Such compounds are abound in nature and industry, e.g. paraffins in swamps, olefins in forests and alkyl lead in automobile exhaust.

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