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Butyl Group

Butyl compounds, Butyl alcohols

Butyl group consists of the group of atoms C₄H₉^- . It is derived by removing one hydrogen atom from either of the isomers of butane, C₄H₁₀, and exists in four isomeric forms. Two isomers of butane exist, n-butane, also called 1–butane (CH₃CH₂CH₂CH₃), and iso-butane, also called 2-methylpropane (CH₃CH(CH₃)CH₃).

Removing a hydrogen atom from the first isomer can result in the formation of two different butyl groups, one designated as n-butyl, and the other as sec-butyl (secondary butyl). The structure of the n-butyl group is CH₃CH₂CH₂CH₂^- ; the structure of the sec-butyl group is 2 CH₃CH CH(CH - 3) . The difference is that the n-butyl group

**TABLE 1. BUTYL COMPOUNDS AND USES**
Compound	Use
n–butyl acetate	manufacture of photographic film, safety glass, artificial leather, perfumes, and flavoring agents
N–butyl pthalate	insect repellant
n–butyltrichlorosilane	production of silicones
4–tert–butyl catechol	used to slow down or stop polymerization reactions in the production of certain plastics and synthetic rubbers
butylate (bis [2–methyl–propyl] carbamothoic acid S–ethyl ester) herbicide t–butyl acetate	gasoline additive
4–tert–butylphenyl salicylate	light absorber in plastic food wrappings
n–butylamine	raw material in the synthesis of many products, including dyes, pharmaceuticals, insecticides, and rubber chemicals
sec–butylamine	prevents the growth of fungi
n–butyl citrate	anti–foaming agent; plasticizer; manufacture of inks and polishes
1–butyl–3–metanilyurea	treatment of hypoglycemia (an abnormally low blood sugar level)
butylmethoxydibenzoyl–methane	screens out ultraviolet light
t–butyl nitrate	jet propellant
n–butyl strearate	used to soften cosmetics, plastics, textiles, and other types of polymers

bonds to other atoms via an end carbon atom, while the sec-butyl group bonds via an "inner" carbon atom.

Removal of a hydrogen atom from the iso-butane isomer can result in the formation of two different butyl groups. One of these groups is commonly known as tertbutyl or 1, 1-dimethylethyl [(CH₃)₃C^- ]. The tertprefix stands for tertiary, indicating that the open bond is from a carbon atom that is attached to three other carbon atoms. The other butyl group that can be formed from iso-butane is the isobutyl or 2-methylpropyl group [(CH₃)₂CHCH₂^- ].

A large number of compounds containing the butyl group exist. Many of them are relatively simple and can be represented by the formula C₄H₉X, where X stands for a halogen, a hydroxyl group, an amine, or some other group. The following sections review some of the most important of these compounds.

Four butyl alcohols exist, each formed by the addition of a hydroxyl group (OH) to one of the four butyl isomers discussed above. Their names and structures are as follows: n-butyl alcohol (or 1-butanol) CH₃CH₂CH₂CH₂OH; iso-butyl alcohol (or 2-methyl-1-propanol) (CH₃)₂CH CH₂OH; sec-butyl alcohol (or 2-butanol) CH₃CHOHCH₂CH₃; tert-butyl alcohol (or 2-methyl-2-propanol) (CH₃)₃COH.

The boiling points of the butyl alcohols decrease regularly in moving down the above list, from 244°F (118°C) for n-butyl alcohol to 226°F (108°C) for isobutyl alcohol to 212°F (100°C) for sec-butyl alcohol to 180°F (82°C) for tert-butyl alcohol. A similar pattern exists for solubility of the alcohols, increasing from 8 g per 100 g of water for n-butyl alcohol to 10 g per 100 g of water and 12.5 g per 100 g of water for the next two forms to complete miscibility for tert-butyl alcohol.

The four butyl alcohols undergo very different reactions in many instances. As an example, n-butyl and isobutyl alcohol can be oxidized rather easily to yield aldehydes. Oxidation of sec-butyl alcohol, however, results in the formation of a ketone. Oxidation of tert-butyl alcohol occurs only under the most extreme conditions, resulting in the complete oxidation of the compound to carbon dioxide and water.

Of the four butyl alcohols, n-butyl alcohol is in the greatest demand commercially. It is used as a solvent for fats, waxes, gums, shellac, varnish, and other materials in many industrial processes. It is also used as the starting point in the preparation of other butyl compounds. All of the butyl alcohols are of some interest in the synthetic flavoring industry since they can react with organic acids to make pleasant smelling esters. For example, n-butyl butanoate has the odor of pineapple; 2-methylpropyl propanoate smells like rum; 2-methylpropyl methanoate, like apple; n-butyl methanoate, like banana; and n-butyl ehtanoate, like strawberry.

The accompanying table summarizes some butyl compounds and their most important uses.

Resources

Books

Budavari, Susan, ed. The Merck Index. 11th ed. Rahway, NJ: Merck and Company, 1989. pp. 236-242.

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

Hawley, Gessner G., ed. The Condensed Chemical Dictionary. 9th edition. New York: Van Nostrand Reinhold, 1977, pp. 133-142.

Loudon, G. Mark. Organic Chemistry. Oxford: Oxford University Press, 2002.

KEY TERMS

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Aldehydes: —A class of organic chemical compounds that contain a -CHO group.
Alkyl group: —A paraffinic hydrocarbon group that may be obtained from an alkane by removing a hydrogen atom from the latter.
Antioxidant: —Any substance that prevents oxidation from occurring.
Copolymer: —A compound with high molecular weight formed in the reaction between two different raw materials.
Esters: —A family of organic compounds formed in the reaction between an alcohol and an organic acid.
Food additive: —A substance added to prepared foods to keep them from spoiling, add flavor or odor, increase their nutritional value, or make some other commercially desirable change in the food.
Herbicide: —A chemical that kills entire plants, often selectively.
Inhibitor: —Any substance that prevents some form of chemical reaction from taking place.
Isomers: —Two molecules in which the number of atoms and the types of atoms are identical, but their arrangement in space is different, resulting in different chemical and physical properties.
Ketones: —A family of organic compounds characterized by the presence of the C=O group appearing anywhere except at the end of the molecule.
Polymerization: —A chemical reaction in which small molecules react with each other over and over many times, forming very large product molecules.
Silicone: —A large group of organic compounds whose molecules consist of organic groups attached to silicon atoms.

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