Paraldehyde decomposition

Paraldehyde decomposition is represented by (CH3CHO)3 ———> 3CH3CHO. The stoichiometry of the reaction is of the form A — ->3B. Assuming that the reaction is first order, then the rate equation for a constant volume batch system is ... 

On acetylation it gives acetanilide. Nitrated with some decomposition to a mixture of 2-and 4-nitroanilines. It is basic and gives water-soluble salts with mineral acids. Heating aniline sulphate at 190 C gives sulphanilic add. When heated with alkyl chlorides or aliphatic alcohols mono- and di-alkyl derivatives are obtained, e.g. dimethylaniline. Treatment with trichloroethylene gives phenylglycine. With glycerol and sulphuric acid (Skraup s reaction) quinoline is obtained, while quinaldine can be prepared by the reaction between aniline, paraldehyde and hydrochloric acid. 

The decomposition of gaseous paraldehyde into gaseous acetaldehyde, which may be represented by the equation, A => 3B, has been followed at 260°C by observing the change in total pressure with time, t in hrs, 7r in Torr. Find the order of the reaction. 

Acetaldehyde also polymerises gradually on keeping, yielding the liquid paraldehyde (CH3.CHO)3, which boils without decomposition at 124°. If a little hydrogen chloride is passed, with cooling, into acetaldehyde the likewise polymeric metaldehyde crystallises out. 

It has been known for a long time that decomposition and polymerization processes occur as a result of irradiation of acetaldehyde. The polymerization process, diminishing in importance towards shorter wavelengths, is induced by free radicals. Iodine traps the free radicals, therefore, no polymerization is observed in the iodine-inhibited reaction . Woolgar and Allmand suggested that the polymer formed was probably paraldehyde. On account of insufficient data, a detailed discussion of the polymerization processes is not justified. 

The roles of manganese in TPA manufacture are better understood than in the Witten process, and include decomposition of the CH2COOH radical (derived from the acetic acid solvent) and regeneration of the bromine atom promoter [13], In an effort to eliminate halogen compounds which are highly corrosive to oxidation equipment, use of acetaldehyde [14] and paraldehyde [15] has been developed. These aldehyde promoters are ultimately converted to acetic acid in high yield. For economic reasons, these aldehyde processes have been abandoned in favor of the bromine-promoted Amoco process. 

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