Cyclobutanone
# Cyclobutanone

Cyclobutanone is an organic compound with molecular formula $(CH_2)_3CO.$ It is a four-membered cyclic ketone (cycloalkanone). It is a colorless volatile liquid at room temperature. Since cyclopropanone is highly sensitive, cyclobutanone is the smallest easily handled cyclic ketone.

## Preparation

The Russian chemist Nikolai Kischner first prepared cyclobutanone in a low yield from cyclobutanecarboxylic acid. Kischner's process, involving several steps, is cumbersome and inefficient; more efficient, high-yielding syntheses have since been developed.

One strategy involves degradation of five-carbon building blocks. For example, the oxidative decarboxylation of cyclobutanecarboxylic acid was improved by the use of other reagents and methods.

A newer, more efficient preparation of cyclobutanone was found by P. Lipp and R. Köster in which a solution of diazomethane in diethyl ether is reacted with ketene. This reaction is based on a ring expansion of the cyclopropanone intermediate initially formed, wherein molecular nitrogen is split off:

The reaction mechanism was confirmed by a reaction using $^{14}C-labeled$ diazomethane.

Another synthesis of cyclobutanone involves lithium-catalyzed rearrangement of oxaspiropentane, which is formed by epoxidation of the easily accessible methylenecyclopropane:

Cyclobutanone can also be prepared in a two step procedure by dialkylation of 1,3-dithiane with 1-bromo-3-chloropropane followed by deprotection to the ketone with mercuric chloride $(HgCl_2)$ and cadmium carbonate $(CdCO_3).$

## Reactions

At about 350 °C, cyclobutanone decomposes into ethylene and ketene. The activation energy for this [2+2] cycloelimination is 52 kcal/mol. The reverse reaction, the [2+2] cycloaddition of ketene and ethylene, has never been observed.

    Decomposition of cyclobutanone
