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ParabenPreservative Also known as paraben, it is a colorless crystal or white crystalline powder, odorless , odorless. The antiseptic effect is better than that of benzoic acid and its sodium salt, the usage amount is only 1/10 of it, and the usage range is pH 4~8. The disadvantage is that parahydroxytoluate preservatives have poor water solubility, and alcohols are commonly used to dissolve them before use, and they are also more expensive.
The maximum allowable usage amount of ethyl paraben is 0.25g/kg for soy sauce; the maximum allowable usage amount of propyl paraben is used for refreshing beverages 0. 10g/kg; 0.012g/kg for fruit and vegetable skins; 0.20g/kg for fruit juice and jam. The allowable daily intake (ADI) is 10 mg/kg body weight.
Production of parabens
There are currently two main methods for producing parahydroxytoluate in industry, namely the esterification method and the one-step method.
The esterification method uses phenol as raw material in the presence of a small amount of water to first generate potassium phenolate, which undergoes an acidification reaction with CO2 to generate phenol-formic acid. The corresponding alcohol reacts to obtain the esterification product.
One-step method is to synthesize parahydroxybenzoate preservative from benzoic acid, potassium carbonate, formic acid, and carbon monoxide in the next step under the action of catalyst. This method reacts The process is simple and the equipment investment is low, but the reaction effect is worse than the first method. Therefore, the following will mainly discuss the ester process. The process flow is shown in Figure 2-2,
The raw material phenol from storage is mixed with the iron mixer(3) Potassium hydroxide is mixed with a small amount of water and heated to generate potassium benzoate, which is then sent to the autoclave(6) and heated to 130~140°C under vacuum. , completely remove excess phenol and moisture to obtain dry phenol methyl salt, introduce carbon dioxide, and carry out the carboxylation reaction. Due to the intense reaction at the beginning, cooling water is used to transfer the reaction heat. As the reaction proceeds, the reaction weakens in the later stages, requiring an external Heating, the temperature is controlled at 180~210℃, and the reaction time is 6~8h. After the reaction is completed, remove the carbon dioxide and add hot water to dissolve it to obtainpotassium p-hydroxybenzoateSolution. The solution is decolorized with activated carbon and zinc powder in the wooden decolorization tank (7), filtered with a filter press (8) while hot, and then p-hydroxybenzoic acid is precipitated in the wooden sedimentation tank (9) with sulfuric acid. The precipitated slurryliquid is centrifuged, washed, and dried to obtain industrial parahydroxybenzoic acid.
Parahydroxybenzoic acid, ethanol, benzene and concentrated sulfuric acid are sequentially added to the esterification kettle. Stir and heat. The steam condenses through the condenser and then enters the water separator. Flow the upper layer of benzene into the esterification kettle. When the distillate no longer contains water, it is the end point of esterification. Switch the condensate outflow switch to steam out the remaining benzene and ethanol. After the temperature in the reaction kettle rises to 100°C, maintain it for 10 minutes. When it is found that no condensate flows out, put the reaction solution into a cleaning pot filled with water and stir rapidly while it is still hot. Add NaOH to wash away the unreacted p-hydroxybenzoic acid. The crystals after centrifugal filtration are then transferred to the cleaning pot, washed twice with clean water, and moved to the decolorization pot. After heating and dissolving with ethanol, add activated carbon to decolorize, press and filter while it is hot and enter the crystallization tank for crystallization. After crystallization and filtration, the product is obtained.
