Patent GB-853621-A (GB)
Title: Improvements in the synthesis of acrylic esters
IPC: C07C51/14
Filed: 1957-02-11
Abstract: An acrylic ester is obtained by simultaneously feeding acetylene and carbon monoxide in a molar ratio of from 1,35:1 to 2:1, nickel carbonyl and hydrogen chloride in stoichiometric ratio and an excess of an alcohol to a reactor having therein a reaction medium containing the alcohol and nickel carbonyl, the nickel carbonyl concentration being maintained at from 0,5 to 13% by weight, the initiation of ester production in the reactor being effected in the presence of the acetylene and the carbon monoxide.  During the initition of ester production the molar ratio of acetylene to carbon monoxide in the gaseous feed is preferably from 1,75 : 1 to 2 : 1 and subsequently conveniently from 1,35 : 1 to 1,55 :1.  The nickel carbonyl concentration is most suitably maintained at 2-6% by weight and the reaction medium is preferably maintained at 35-65 DEG  C. and at normal pressure.  The process may be carried out continuously or batchwise and the presence of polymerisation inhibitors is advisable particularly during the separation and purification of the acrylic ester.  The reactor may contain the ester to be produced and/or nickel chloride which has been produced in a similar process before the acetylene and carbon monoxide are fed thereto.  It is preferable, until the reaction has started, to introduce acetylene and carbon monoxide at a lower rate than that required in the later stages of the process.  Advantageously reaction medium is continuously withdrawn from the reactor, and fed to a stripping unit, preferably kept at 10-60 DEG  C. where it is stripped of all the nickel carbonyl and a large proportion of its alcohol content together with some ester, by means of a stream of gas, advantageously passed countercurrently to the liquid, comprising acetylene and/or carbon monoxide, preferably an acetylene/carbon monoxide mixture or carbon monoxide alone which then passes into the reactor, forming part or all of the gaseous reactant feed.  The liquid product from the stripping unit is then submitted to subsequent treatment, for purification of the acrylic ester, recovery and recycling of that part of the alcohol still present, and regeneration of nickel carbonyl from the corresponding chloride.  The process can be used for the preparation of acrylic esters of aliphatic alcohols, arylaliphatic alcohols or cycloaliphatic alcohols.  When using amyl alcohol or an alcohol of higher molecular weight it is necessary in order to maintain the reaction mass sufficiently fluid, to add a preferably lowboiling inert solvent.  It is preferred to introduce the reactants at different points of the reactor which is preferably in the form of a closed circuit.  The nickel carbonyl and alcohol can be introduced into the circuit at any point, but preferably downstream from the point at which the reaction product is withdrawn. The HCl must be introduced in advance of or at the point of introduction of the gases.  The nickel carbonyl may be introduced into the gaseous phase.  It is necessary to remove part of the reaction heat by cooling in order to maintain the temperature at a constant value.