An investigation into the use of ultrasound in the synthesis of fine chemicals

The application of ultrasound to the oxidative dimerisation of pivalic acid to tetramethyladipic acid (TMAA; 2,2,4,4-tetramethylhexa-1,6- dioic acid) using Fenton's reagent is described. Various parameters of the reaction were investigated (gas, equivalents of reagents, temperature, and sonication) and their effect on the yield of TMAA is discussed. Separation of the reaction mixture into TMAA (dimer) and the trimers and tetramers was achieved. The reaction conditions were optimised using experimental design, and statistical analysis illustrates the significant factors that affect the yield. Optimal reaction conditions for the production of TMAA were found to be 0.17 equivalents of Fenton's reagent, high dilution no ultrasound, under nitrogen. Alternative sources of hydroxyl radicals in organic solvents were also investigated The production of 3-bromothiophene (3BT) from the rearrangement of 2,5 -dibromothiophene and reduction of 2,3,5-tribromothiophene was investigated. Ultrasound, reaction time and temperature all have an effect on the yield and selectivity in the synthesis of 3BT. Ultrasound was found to have a modest effect on the yield of 2-methoxythiophene from 2-bromthiophene using sodium methoxide with several catalyst systems (Cu, CuO, CuO/KI, CuO/KI/Copper acetyl acetonate). 2-Bromothiophene was used as a substrate in attempted Wurtz-type coupling reaction conditions. These reactions produced complex mixtures of bromothiophenes via halogen rearrangements. The silylation of bromothiophenes was successfully achieved using several bromothiophene substrates under quiet and sonicated conditions with various reaction times and equivalents of reagents. A calorimetry study on the acoustic output of the ultrasonic probe provided data at different temperatures, depths, solvents, and power settings. The resultant data was in strong agreement with previously published work.