Patent GB-654663-A (GB)
Title: Pyrolysis of unsaturated ethers
IPC: A23K1/10
Filed: 1947-08-06
Abstract: Unsaturated aldehydes are made by pyrolysing an ether derived from an unsaturated primary alcohol having an olefinic linkage in a non-vinyl position with respect to the oxygen atom or derived from such an alcohol and another alcohol which may be primary or secondary, saturated or unsaturated, provided that it does not contain an olefinic linkage in vinyl position with respect to the oxygenation, in the vapour state and at a temperature of between 300 DEG  C. and the temperature at which substantial decomposition of the unsaturated aldehyde obtained occurs, said unsaturated aldehydes having a structure similar to that of the ethers from which they are derived. Ethers used preferably contain radicles in both of which the olefinic linkage occurs in the allyl position with respect to the carbon atoms attached to the ether oxygen atom.  Highest yields are obtained from symmetrical ethers.  Many ethers are specified including di-allyl, methyl - allyl, isopropyl - allyl, di-methallyl, methyl-phenallyl and methyl-4-cyclohexyl-2,3-butenyl.  Cleavage may occur at either side of the ether oxygen atom so that a mixture of products may result including hydrocarbons, thus dimethallyl ether yields methacrolein and isobutylene, ethyl-allyl ether yields an unsaturated and saturated aldehyde with hydrocarbons and ethers derived from a primary and a secondary alcohol yield mixtures of aldehydes, ketones and hydrocarbons.  The temperature of pyrolysis will depend on the ether used and the flow rates chosen, for diallyl or dimethallyl ethers temperatures instanced are 500-650 DEG  C., preferably 550-600 DEG  C.  Preferably atmospheric or superatmospheric pressures are used, although low pressures are effective.  Diluents, e.g. nitrogen or steam, may be present so that the aqueous azeotropes obtained in the manufacture of ethers may be used.  The reactors are preferably packed with heat-transferring material such as quartz or glass chips, brass turnings and silver gauze.  In examples: (1) preheated dimethallyl ether is pyrolysed in a stainless steel tube at 500-570 DEG  C. with a flow rate of 0.5 c.cs. per minute, the products being condensed in an ice-cold reflux condenser and overhead gases collected over saturated brine, fractionation of the condensate yielding methacrolein; (2) dimethallyl ether vaporized in an aluminium preheater is pyrolysed in a hard glass tube at 580-600 DEG C. with a flow rate of 2.5-3.0 c.cs. per minute, methacrolein being recovered as before; and (3) diallyl ether at about 1065 grams per hour is passed at about 575 DEG  C. through a steel tube packed with quartz chips to yield acrolein and propylene.  In the Specification as open to inspection under Sect. 91 unsaturated aldehydes and ketones are made by pyrolysing symmetrical and/or unsymmetrical, primary and/or secondary ethers containing an olefinic linkage in non-vinyl position with respect to the ether oxygen atom.  When one of the radicles is attached to the ether oxygen atom by means of a methylene radicle, i.e. is of primary structure, and also contains an olefinic linkage in allyl position with respect to that oxygen atom the product contains unsaturated allyl type aldehydes.  Pyrolysis of secondary ethers of the above allyl type, many of which are specified, gives allyl type unsaturated ketones.  The ethers used may be substituted, e.g. with halogens, and contain heterocyclic groups. This subject-matter does not appear in the Specification as accepted.