Methylparaben CAS 99-76-3

The sulfonic acid catalyzed synthesis of ethyl p-hydroxybenzoate can be divided into p-toluenesulfonic acid, sulfamic acid, strong acid cation exchange resin to synthesize ethyl hydroxybenzoate.

1. p-toluenesulfonic acid p-toluenesulfonic acid is a strong organic acid, its corrosion to equipment and three waste pollution are less than sulfuric acid, it is not easy to cause other side reactions, the product has good color and luster, cheap and easy to obtain, easy to store, transport and use , with less dosage and high activity, it is a good catalyst to replace sulfuric acid and can be suitable for industrial production.
2. Sulfamic acid Sulfamic acid (H2N-SO2OH), like p-toluenesulfonic acid, is a cheap, easy-to-obtain and stable crystal. It is convenient and safe to transport, store, and use. The difference is that it is insoluble in the organic reaction system, so it has little corrosion to equipment, high yield of synthetic products, and the separated sulfamic acid can be used repeatedly for catalytic use. Good catalyst for ethyl esters. When the molar ratio of p-hydroxybenzoic acid and ethanol is 1:4, sulfamic acid is 10.3% of the total amount of reactants, and the water is refluxed for 3 hours, the yield of ethyl p-hydroxybenzoate reaches 90.38%.
3. Strong acid cation exchange resin Strong acid cation exchange resin is a kind of polymer sulfonic acid, which is cheap and easy to obtain, has no corrosion to equipment, does not pollute the environment, does not cause side reactions, and is insoluble in the reaction system, easy to recover, It can be reused and regenerated, is easy to operate, is a good environment-friendly catalyst, and has industrial use value.

The uniqueness of inorganic catalysis is that its catalysis varies with different compounds, and it is not catalyzed by protic acids like sulfonic acid catalysis. There is a large class of inorganic substances that are inexpensive and readily available Lewis acids, whose metal atoms have empty orbitals that can coordinate with the carbonyl oxygen in carboxylic acids, thus catalyzing esterification. At the same time, they have less corrosion to equipment, less environmental pollution and less catalyst consumption, and are good catalysts for the synthesis of certain esters.

1. Lewis acid catalysis Zhang Nairu et al. discussed the synthesis of ethyl p-hydroxybenzoate catalyzed by neodymium trioxide. When 0.1mol p-hydroxybenzoic acid, 0.5mol ethanol, 1.2g catalyst (6% of the acid amount), reflux heating for 4h , the product yield is 78.4%. The catalyst is insoluble in the reaction system, can be reused, does not corrode equipment, does not pollute the environment, and is a catalyst with practical value.

2. Protic acid catalyzed sodium bisulfate monohydrate (NaHSO4·H2O) is also a good esterification catalyst. It is also a cheap, easy-to-obtain and stable crystal, and its aqueous solution is strongly acidic. Due to the presence of H+ in the ionization of HSO-4, it belongs to the catalysis of protic acid and can catalyze the synthesis of ethyl p-hydroxybenzoate, and the yield of the product is 91.5 %. The microwave radiation was introduced into the reaction, when 0.1mol p-hydroxybenzoic acid, 0.4mol ethanol, 0.4g catalyst, 522W microwave radiation was used for 7min, the product yield reached 83.0%, which greatly accelerated the reaction.

Superacids are acids with stronger acid strength than 100% sulfuric acid. Solid super acid has the advantages of not corroding equipment, not polluting the environment, not afraid of water, high temperature resistance, high reactivity, good selectivity, easy preparation, easy separation from the reaction system, convenient operation, not easy to poison, easy to recover, reuse and regenerate. , is an excellent environment-friendly catalyst. Since Hino et al. first synthesized new solid superacids such as TiO2/SO2-4 in 1979, research and development applications have been very active. This SO2-4/MxOy solid superacid has also been widely used in the synthesis of ethyl p-hydroxybenzoate.