Benzoic+Acid

Benzoic acid C 6 H 5 COOH It is colorless, a crystalline solid and the simplest aromatic carboxylic acid. the name derived from gum benzoin, which was for a long time the only source for benzoic acid. Its salts are used as a food preservative and benzoic acid is an important precursor for the synthesis of many other organic substances. The salts and esters of benzoic acid are known as benzoates. It has a molecular weight of 122.12 g/mol It is manufactured by treating molten ophthalmic anhydride with steam in the presence of a zinc oxide catalyst, by the hydrolysis of benzotrichloride, or by the oxidation of toluene with nitric acid or sodium bicarbonate or with air in the presence of a transition metal salt catalyst. It is almost exclusively manufactured by the cobalt catalyzed liquid-phase air oxidization or toluene. Benzoic acid's production and use as a plasticizer, food preservative, and tobacco seasoner may result in its release to the environment through various waste streams. However, benzoic acid occurs in nature in free and combined forms.

USES

 * Benzoic acid is the most commonly used chemical standard to determine the heat of capacity of a bomb calorimeter.
 * Benzoic acid is used to make a large number of chemicals, such as Benzoyl Chloride, benzoate plasiticizers, and phenol.
 * Benzoic acid and its salts are used as a food preservatives.
 * Benzoic acid is used for the treatment of fungal skin diseases.[|8][|]]

Industrial preparations
Benzoic acid is produced commercially by partial oxidation of toluene with oxygen. The process is catalyzed by cobalt or manganese naphthenates. The process uses cheap raw materials, proceeds in high yield, and is considered environmentally green. U.S. production capacity is estimated to be 126,000 tonnes per year (139,000 tons), much of which is consumed domestically to prepare other industrial chemicals.

Laboratory synthesis
Benzoic acid is cheap and readily available, so the laboratory synthesis of benzoic acid is mainly practiced for its pedagogical value. It is a common undergraduate preparation. For all syntheses, benzoic acid can be purified by recrystallization from water because of its high solubility in hot water and poor solubility in cold water. The avoidance of organic solvents for the recrystallization makes this experiment particularly safe. Other possible recrystallization solvents include acetic acid ( anhydrous or aqueous), benzene, acetone, petroleum ether, and a mixture of ethanol and water. The solubility of benzoic acid in over 40 solvents with references to original sources can be found as part of the Open Notebook Science Challenge

By hydrolysis
Like any other nitrile or amide, benzonitrile and benzamide can be hydrolyzed to benzoic acid or its conjugate base in acid or basic conditions.

From benzaldehyde
The base-induced disproportionation of benzaldehyde, the Cannizzaro reaction , affords equal amounts of benzoate and benzyl alcohol ; the latter can be removed by distillation.

From bromobenzene
Bromobenzene can be converted to benzoic acid by "carbonation" of the intermediate phenylmagnesium bromide C6H5MgBr + CO2 → C6H5CO2MgBrC6H5CO2MgBr + HCl → C6H5CO2H + MgBrCl

From benzyl alcohol
Benzyl alcohol is refluxed with potassium permanganate or other oxidizing reagents in water. The mixture is hot filtered to remove manganese dioxide and then allowed to cool to afford benzoic acid.

From benzyl chloride
Benzoic acid can be prepared by oxidation of benzyl chloride in the presence of alkaline KMnO4: C6H5CH2Cl + 2 KOH + 2 [O] → C6H5COOK + KCl + H2O

Historical preparation
The first industrial process involved the reaction of benzotrichloride (trichloromethyl benzene) with calcium hydroxide in water, using iron or iron salts as catalyst. The resulting calcium benzoate is converted to benzoic acid with hydrochloric acid. The product contains significant amounts of chlorinated benzoic acid derivatives. For this reason, benzoic acid for human consumption was obtained by dry distillation of gum benzoin. Food-grade benzoic acid is now produced synthetically.

**__ Health Hazards & Environmental Hazards __**
The dust might irritate the nose and eyes. If heated, the fumes might irritate the skin and respiratory system. Benzoic acid is harmful to aquatic life in very small quantities. Collect any waste material for proper disposal. Sweep spilled material and do not flush down the drain.

Read more: [|Safety Information for Benzoic Acid | eHow.com] [|http://www.ehow.com/facts_5459064_safety-information-benzoic-acid.html#ixzz1uKFb0MLF]