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Pentyl Group

carbon atom amyl atoms

Pentyl is the name given to the portion of an organic molecule that is derived from pentane and has the molecular structure -CH2CH2CH2CH2CH3. The pentyl group is one of the alkyl groups defined by dropping the -ane ending from the parent compound and replacing it with - yl. The pentyl group is derived from pentane (HCH2CH2CH2CH2CH3) by removing one of the end hydrogens. The parent compound consists of five carbon atoms connected by single bonds (C-C) and each carbon atom is connected to a variable number of hydrogen atoms (C-H). The number of C-H bonds formed is dependent on the carbon atom's chain position, with each of the five carbon atoms having a total of four bonds. The name pentane is derived from the Greek word, pente, which means five. There are three other similar five carbon atom containing alkyl groups. The isopentyl group has the molecular structure of -CH2CH2CH(CH3)2 and is identified as a pentyl derivative that has a methyl group (-CH3) branching from the end of a chain of four carbon atoms. The neopentyl group is a chain of three carbon atoms with two methyl groups attached to the end carbon atom and is represented by -CH2C(CH3)3. Similarly, the tert-pentyl group, -C(CH3)2CH2CH3 is a five carbon atom alkyl group that has two carbon atoms bonded to the attaching carbon atom. Pentane is a low boiling liquid that is found in natural gas and crude oil. It can be obtained by liquefying the vapors formed from heating crude oil. Pentane and the similar five carbon atom compound, isopentane, are both the components of gasoline. Pentane has an octane number of 62 and 93 is the octane number for isopentane. Pentane when mixed with red dye is used as the fluid in thermometers that measure very cold temperatures.

Pentyl or five carbon atom alkyl groups are also referred to as amyl groups. The term amyl is derived from the Latin word for starch, amylum, and is used because the five carbon atom amyl alcohols were first isolated from fermentation products. Amyl or pentyl alcohols consist of a chain of five carbon atoms with a hydroxyl group (-OH) connected to one of the carbon atoms. Each carbon atom is also connected to enough atoms resulting in each carbon atom having a total of four bonds. If the hydroxyl group is connected to the first carbon atom, the compound is called n-amyl alcohol or 1-pentanol. Secamyl alcohol or 2-pentanol has the hydroxyl group connected to the second carbon atom and 3-pentanol has the -OH connected to the third carbon atom. Amyl alcohols are used in the manufacture of lubricants, fragrances, flavors, solvents, and other important chemicals. For example, n-amyl alcohol is industrially converted into zinc diamyldithiophosphate and zinc diamyldithiocarbamate compounds, which are additives of grease and motor oil since they slow the wear and deterioration of metal parts. Amyl alcohol can also be converted to amyl bromide, an important chemical in the photographic industry. It can be chemically converted into the cyclic ester, octalactone. Octalactone is a synthetic coconut flavor additive of various foods and is an ingredient found in many floral smelling perfumes. Amyl salicylate, another compound prepared from amyl alcohol, is used extensively in the manufacture of perfumed soaps.

The compounds prepared from amyl alcohols are not the only commercially important compounds that contain a pentyl group. Amyl mercaptan has a thiol group (-SH) connected to a chain of five carbon atoms. Amyl mercaptan is also commonly referred to as "Pentalarm" which is added to natural gas to give it a skunk-like smell. Natural gas has no odor and without the addition of amyl mercaptan, a gas leak would be undetectable.


Resources

Books

Arctander, S. Perfume and Flavor Materials of Natural Origin. New Jersey: Arctander, Elizabeth, 1960.

Carey, Francis A. Organic Chemistry. New York: McGraw-Hill, 2002.

Kirk-Othmer. Encyclopedia of Chemical Technology. "Amyl Alcohols. Vol. 2. "Hydrocarbons." Vol. 13. New York: John Wiley and Sons, 1991.


Andrew Poss

KEY TERMS

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Isopentyl group

—An alkyl group with the molecular structure of -CH2CH2CH(CH3)2 and is identified as the pentyl derivative that has a methyl group (-CH3) branching from the end of a chain of four carbon atoms.

Neopentyl group

—A chain of three carbon atoms with two methyl groups attached to the end carbon atom and is represented by -CH2C(CH3)3.

Pentane

—The compound whose molecular structure is CH3CH2CH2CH2CH3 and consists of five carbon atoms connected by single bonds (C-C) and each carbon atom is connected to enough hydrogen atoms (C-H) to have a total of four bonds each.

Pentyl group

—The name given to the portion of an organic molecule that is derived from pentane and has the molecular structure -CH2CH2CH2CH2CH3.

Tert-pentyl group

—An alkyl group with the molecular structure of -C(CH3)2CH2CH3 and is identified as the five carbon atom alkyl group that has two carbon atoms bonded to the attaching carbon atom.

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