Acyl chlorides (also known as acid chlorides) are one example of an acid derivative. In this case, a chlorine atom has replaced the-OH group. The acyl group is a hydrocarbon group attached to a carbon-oxygen double bond. Acid chlorides (also known as acyl chlorides) have the functional group:
The suffix of acyl chloride is -oyl. For example, if the R group is CH3, it would be called ethanoyl chloride.
· Boiling Points: Most acid chlorides are volatile liquids at room temperature, but boiling point increases as length of the carbon chain increases, due to increased London forces. They also have dipole-dipole attractions, as they are polar molecules.
· Solubility: They are soluble in several organic solvents, but react with water (often violently) so can’t be dissolved in it.
Acid chlorides are prepared from carboxylic acids. The –OH group is replaced by a chlorine atom.The reagents that can be used are phosphorus pentachloride, phosphorus trichloride or thionyl chloride. Starting from ethanoic, and producing ethanoyl chloride, the equations are:
CH3COOH +PCl5 ⇨ CH3COCl + POCl3 + HCl
3 CH3COOH+ PCl3 ⇨ 3 CH3COCl + H3PO3
CH3COOH +SOCl2 ⇨ CH3COCl + SO2 + HCl
The reactions of alcyl chlorides are affected by:
- The strength of the C-X bond
- The stability of the X leaving group. The C-Cl bond is not very strong and Cl- is a good leaving group.
- The molecule is very susceptible to nucleophilic attack in an addition elimination mechanism. The nucleophile replaces the Cl atom
Acid chlorides, like carboxylic acids and esters, are reduced by lithium tetrahydridoaluminate (III) in dry ether solution to form a primary alcohol, e.g.
CH3COCl + 4[H] ⇨ CH3CH2OH + HCl
Drafted by Eunice (Chemistry)