Butyl Mercaptan

KEY FACTS

OTHER NAMES:

Three forms of butyl mercaptan exist; see Overview

FORMULA:

C₄H₁₀S

ELEMENTS:

Carbon, hydrogen sulfur

COMPOUND TYPE:

Mercaptan (organic)

STATE:

Liquid

MOLECULAR WEIGHT:

90.19 g/mol

MELTING POINT:

Forms vary greatly; see Overview

BOILING POINT:

Forms vary; see Overview

SOLUBILITY:

Insoluble or slightly soluble in water (depending on form); soluble in alcohol and ether

OVERVIEW

Three isomers of butyl mercaptan (BYOO-til mer-KAP-tan) exist. Isomers are two or more forms of a chemical compound with the same molecular formula, but different structural formulas and different chemical and physical properties. The names and synonyms of the isomers are: n-butyl mercaptan, known as 1-butanethiol, 1-mercapto-butane, or n-butyl thioalcohol; sec-butyl mercaptan, called 2-butanethiol or 1-methyl-1-propanethiol; and tert-butyl mercaptan, also known as 2-methyl-2-propanethiol. The isomers have slightly different expanded chemical formulas: n-butyl mercaptan, CH₃CH₂CH₂CH₂SH; sec-butyl mercaptan, CH₃CH₂CH(SH)CH₃; and tert-butyl mercaptan, CH₃C(CH₃)(SH)CH₃. The isomers have vastly differing melting points: n-butyl mercaptan, −115.67°C (−176.21°F); sec-butyl mercaptan, −165°C (−265°F); and tert-butyl mercaptan, −0.5°C(31°F). Boiling points differ, but not as greatly: n-butyl mercaptan, 98.46°C (209.2°F); sec-butyl mercaptan, 85°C (180°F); and tert-butyl mercaptan, 64°C (150°F).

All three isomers of butyl mercaptan are mobile liquids (liquids that flow easily) with very strong skunk-like odors. At one time, chemists thought that the butyl mercaptans were responsible for the distinctive odor of skunk spray. Research has now shown that some mercaptans are found in skunk spray, but the butyl mercaptans are not among them.

HOW IT IS MADE

A number of methods are available for the production of the butyl mercaptans. The most common method involves the reaction between an iodobutane (a butane molecule with one iodine atom, such as CH₃CH₂CH₂CH₂I) and a sulfhydryl compound, such as KSH. In this reaction, the sulfhydryl group (-SH) replaces the iodine to form the butyl mercaptan.

COMMON USES AND POTENTIAL HAZARDS

More than 500,000 kilograms (1 million pounds) of the butyl mercaptans are produced each year in the United States. Their primary uses are as solvents and in the preparation of other organic compounds, especially insecticides and herbicides. Among their other uses are:

• Additives for natural gas, which normally has no odor, so that leaks can be easily detected;
• As an additive to enhance the flavor and aroma of certain foods;
• Nutrient in the maintenance of bacterial cultures.

Interesting Facts

• The Israeli army reportedly developed a "skunk bomb" containing mercaptans to use as a crowd-control device against Palestinians.
• The Guinness World Records book classifies the butyl mercaptans as being among the two smelliest compounds in the world. The other chemical is ethyl mercaptan.
• The odor of the butyl mercaptans is said to be detectable at a distance of nearly a kilometer (about a half mile) from its source.

All three isomers of butyl mercaptan are highly toxic. Anyone exposed to their vapors should seek medical attention immediately. The compounds are also very flammable and must be handled with care to prevent their catching fire. Since most individuals never come into contact with the butyl mercaptans, their health and safety risks are of concern primarily to workers who handle them in their everyday jobs.

Words to Know

ISOMER

One of two or more forms of a chemical compound with the same molecular formula, but different structural formulas and different chemical and physical properties.

MERCAPTAN

Organic compound that contains a sulfhydryl group (-SH) attached to a carbon.

FOR FURTHER INFORMATION

Bauman, Richard. "Getting Skunked: Understanding the Antics behind the Smell." Backpacker (May 1993): 30-31.

"n-Butyl Mercaptan." International Chemical Safety Cards. http://www.cdc.gov/niosh/ipcsneng/neng0018.html (accessed on September 14, 2005).

"The Stink that Stays." Popular Mechanics (December 2004): 26.

Wood, William F. "Chemistry of Skunk Spray." Humboldt State University. http://www.humboldt.edu/∼wfw2/chemofskunkspray.html (accessed on September 14, 2005).