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1.4 CHEMICAL SCIENCES
The objective of this work was to investigate the process for the production of an organic herbicide, phenmedipham, utilising isobutylacetate as solvent and to scale up the reaction to one litre. This was carried out according to a technical bulletin received from Barclay Plant Protection Ltd. Difficulties were encountered in isolating the product, methyl N-(3-hydroxyphenyl) carbamate, from stage 1 with isobutylacetate as solvent. An investigation of the use of other solvents for the reaction process led to the use of ethyl acetate, in a modified version of the method used by Schering A-G, and resulted in a 93% yield of phenmedipham. In addition an investigation into the synthesis and characterisation of impurities formed, and reported to be formed, in the reaction process was carried out. Two of these impurities were synthesised, and a third was shown not to form in the reaction process. In addition a fourth impurity was identified and characterised The project was carried out in a series of steps (1) Step 1 involved the optimisation of the reaction conditions for stage 1 to a 10g scale. (2) The second step involved the optimisation of stage 2 reaction parameters to a 10g scale. (3) Step three involved researching an alternative solvent system to aid the isolation process in stage 1 and stage 2. (4) Step 4 involved a reaction sequence which was carried out without isolation of the stage 1 product. This resulted in an impurity bring formed in the reaction process which resulted in a low yield of phenmedipham. (5\0 in step 5 a reaction sequence was carried out in which the intermediate methyl n-(3-hyrdoxyphenyl) carbamate was isolated and brought directly to stage 2 without purification. (6) In step 6 attempts were made to reduce the amount of solvent required for the process. (7) Step 7 involved scale up of the reaction process to 30g with respect to the stage 1 product. (8) Step 8 involved the scale up to a 60g scale with respect to m-aminophenol, which required one litre of solvent.
Byrne, M. (1998).Phenmedipham process development. Masters dissertation. Technological University Dublin. doi:10.21427/D7GK6P