inert under the reaction conditions among these are by way of example aliphatic hydrocarbons halogenated aliphatic hydrocarbons and aromatic and substituted aromatic hydrocarbons and ethers it is preferable that the solvent is one selected from pentane hexane heptane ligroin petrol ether cyclohexane dichloromethane trichloromethane tetrachloromethane benzene toluene xylene chlorobenzene dichlorobenzenes dibutyl ether thf dioxane and mixtures thereof the esterification is usually carried out in the temperature range from 50 to 250 u00b0 c if the esterification catalyst is selected from organic acids or mineral acids the esterification is carried out typically in a temperature range from 50 to 160 u00b0 c if the esterification catalyst is selected from amphoteric catalysts the esterification is carried out typically in a temperature range from 100 to 250 u00b0 c the esterification can take place in the absence of or in the presence of an inert gas the expression inert gas generally means a gas which under the prevailing reaction conditions does not enter into any reactions with the starting materials reagents or solvents participating in the reaction or with the resultant products it is preferable that the esterification takes place without addition of any inert gas conventional processes known to the person skilled in the art can be used for the reaction described in steps b1 and c2 of.