Method for producing benzoic acid esters
A process for preparing benzoic esters whose alkoxy groups have from 7 to 13 carbon atoms by reacting benzoic acid with at least one alcohol having from 7 to 13 carbon atoms, the water of reaction formed being removed during the esterification reaction by distillation, and the alcohol not converted in the esterification reaction being removed after the esterification reaction, in which the reaction takes place in the presence of a tin(II) compound as catalyst and, without treatment with a base, the catalyst and/or its derivatives is/are separated off by filtering or by centrifuging from the reaction mixture which remains after the unconverted alcohol has been separated off.
1 . A process for preparing benzoic esters whose alkoxy groups have from 7 to 13 carbon atoms by reacting benzoic acid with at least one alcohol having from 7 to 13 carbon atoms, the water of reaction formed being removed from the reaction mixture during the esterification reaction by distillation with the alcohol used in excess, and the alcohol not converted in the esterification reaction being removed after the esterification reaction,
characterized
in that the reaction takes place in the presence of a tin(II) compound as catalyst at a temperature of 160 to 250° C. and in that, without treatment with a base, the catalyst and/or its tin-containing derivatives are removed by filtering or by centrifuging from the reaction mixture which remains after the unconverted alcohol has been separated off, to an extent such that the tin content of the end product (filtrate) is below 1 mg/kg (ppm) and in that alcohols used are heptanols, 1-octanol, 2-octanol, 2-ethylhexanol, nonanols and/or tridecanols.
2 . The process of claim 1 ,
characterized
in that a mixture of alcohols with the same or different number of carbon atoms is used.
3 . The process of claim 1 ,
characterized
in that the unconverted alcohol is removed by stripping, distilling or steam-distillation or by a combination of two or more of these methods.
4 . The process of at least one of claim 1 ,
characterized
in that the unconverted alcohol is separated off after the esterification reaction by vacuum distillation and subsequent stripping with steam or nitrogen.
5 . The process of claim 1 ,
characterized
in that the catalyst is separated off at a temperature below 160° C.
6 . The process of claim 1 ,
characterized
in that the catalyst and/or derivative(s) thereof is/are separated off from the reaction mixture, after the alcohol has been separated off and without base treatment, by filtration at temperatures below 130° C.
7 . The process of claim 1 ,
characterized
in that the volume of liquid removed from the reaction mixture during the esterification by (azeotropic) distillation is made up in whole or in part with the reactant alcohol or reactant alcohol mixture.
8 . The process of claim 1 ,
characterized
in that the volume of liquid removed from the reaction mixture during the esterification by (azeotropic) distillation is partly recycled, by separation of the liquid separated off into an aqueous phase and an organic phase, and recycling of the organic phase into the esterification reaction.
9 . The process of claim 1 ,
characterized
in that the volume of liquid removed from the reaction mixture during the esterification by (azeotropic) distillation is made up in whole or in part, by separation of the liquid separated off into an aqueous phase and an organic phase and recycling the organic phase, additionally admixed with fresh alcohol, into the esterification reaction.
10 . The process of claim 1 ,
characterized
in that the volume of liquid removed from the reaction during the esterification by (azeotropic) distillation is made up in whole or in part with the fresh alcohol.
11 . The process of claim 1 ,
characterized
in that tin(II) salts of monocarboxylic or dicarboxylic acids are used as catalyst.
12 . The process of claim 1 ,
characterized
in that a molar ratio of tin to benzoic acid of 10 −5 : 1 to 10 −3 : 1 is set at the beginning of the reaction.
13 . The process of claim 1 ,
characterized
in that a polymeric or ceramic membrane, composite membrane or paper filter is used as filter.
14 . The process of claim 1 ,
characterized
in that the benzoic acid is esterified to an acid number of <0.1 mg KOH/g, determined in accordance with DIN EN ISO 2114.
15 . A composition comprising benzoic ester(s) and isononyl benzoate, prepared by a process of claim 1 .
16 . The composition of claim 15 ,
characterized
in that the tin content of the product is below 1 mg/kg.
17 . A method of using the composition of claim 15 in paints, varnishes, adhesives or components of adhesives or as a viscosity reducer and/or plasticizer for PVC.