Clemmensen reaction

Clemmensen reaction is the reduction of carbonyl compounds with amalgamated zinc and concentrated hydrochloric acid... 

Cleavage of carbon-nitrogen bonds adjacent to the carbonyl function can occur during the Clemmensen reaction. In most cases these reactions passed unnoticed until tlie products were re-examined by N. J. Leonard [117]. The processes were termed abnormal Clemmensen reactions. Prior to this work, the only unusual Clemmensen reduction processes noted were of (o-butoxy-2,4-dihydroxy-acetophenone which gives 1-etliyl-2,4-dihydroxybenzene [118] and of co-dimethylaminoacetophenone which gives ethylbenzene and dimetiiylamine [119],... 

The Clemmensen reaction is used mainly with aryl alkyl ketones,... 

The mechanism of this reduction is probably similar to that of the Clemmensen reaction.11... 

Apart from investigations of the mechanism of the Clemmensen reaction ensuing from the formation of 3, work on the reactivity of nitrenes (Section IV,A,4), as well as studies of photochemical rearrangements of acridine Af-oxides (Section IV,B), have led to 4-azaazulenes. 

Chromium trioxide, 21 Clemmensen reaction, 111 18-Crown-6-potassium cyanide complex, 129... 

Chromium trioxide, 60, 21 Clemmensen reaction, 60, 111 Copper chloride (CuCl) [7758-89-6], 61, 122 Crotonic acid, ethyl ester, ( )-, 61, 85 18-Crown-6-potassium cyanide complex, 60,129 Crum Brown-Walker reaction, 60, 4 Cuprous chloride, 60, 42, 121 61, 122 CYANIC ACID, PHENYL ESTER [1122-85-6], 61, 35... 

Reduction of a ketone to a methylene group (CH2)—the Wolff-Kishner or Clemmensen reaction (18.14B)... 

Fletcher and Razaq studied the four-electron reduction of acetophenone to ethylbenzene in strongly acidic media. Such an electroreduction is analogous to the classical Clemmensen reaction, which is carried out with amalgamated zinc in concentrated hydrochloric acid. 

Clemmensen reaction. The Clemmensen method of reduction (1913) consists in refluxing a ketone with amalgamated zinc and hydrochloric acid. Acetophenone, for example, is reduced to ethylbenzene. The method is applicable to the reduction of most aromatic-aliphatic ketones to at least some aliphatic and alicyclic ketones, to the y-keto acids obtainable by Friedel-Crafts condensations with succinic anhydride (succinolylation), and to the cyclic ketones formed by intramolecular condensation. 

Mechanistic Analogies Between the McMuny, Wittig, and Clemmensen Reactions... 

The reaction is commonly carried out in hot concentrated hydrochloric acid with ethanol as a co-solvent. These conditions preclude the presence of acid-sensitive or hydrolyzable functional groups. The Clemmensen reaction works best for aryl ketones and is less reliable with unconjugated ketones. A modification in which the reaction is run in ether saturated with dry hydrogen chloride gave good results in the reaction of steroidal ketones. ... 

The Clemmensen reaction of carbonyl compounds, which requires refluxing for 1-2 days with amalgamated zinc (from 100 gm of mossy zinc, 5 gm mercuric chloride, 5 ml of concentrated hydrochloric acid, and 100-150 ml water) and hydrochloric acid, yields hydrocarbons. 

Reduction of aldehydes or ketones to hydrocarbons can be accomplished using the Clemmensen reaction (Zn/Hg/HCI), the Wolff-Kishner reaction (hydrazine, KOH), Raney nickel/Hj reduction of a dithioacetal, or palladium-catalyzed hydrogenolysis (aryl ketones only). 

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