When making Mitsunobu reaction and Witting reaction, we usually add excessive triphenylphosphine. After the reaction, a large amount of triphenylphosphine is produced. These by-products are mixed with our products, making it difficult for our products to be separated. Triphenoxyphosphine is easily soluble in ethanol, DCM and other solvents. It is less soluble in diethyl ether and petroleum ether. Its Rf value is about 0.1 or less (diethyl ether/petroleum ether =1:1), and its polarity is larger. In the mass spectrum, the signal is very strong. Therefore, strong molecular ion peak and UV absorption peak can be seen in LC-MS. In many cases, the peak pressure of our products will be relatively low.
1. if the input is very small (generally refers to the amount of less than 1 gram), the polarity and raw products have a certain difference, can be removed by column chromatography method of triphenylphosphine oxygen.
2. If the product has acid functional groups that can be formed into salt, then it can be made into corresponding salt. The method of reverse extraction with organic solvent and aqueous phase acidification can remove triphenylphosphine.
3. If the product has alkaline functional groups that can be formed into salt, it can also be treated with reference to method 2.
4.if the product polarity is very small can be extracted with n-hexane or petroleum ether, triphenylphosphine is slightly dissolved in n-hexane and petroleum ether.
5. If it is a good solid, it can be purified by beating or recrystallization.
experience sharing :
We add 20% ethanol aqueous solution first, make it a suspension (if add other solvents, may not be able to form a good suspension, even still remain half solvent oil, compounds in the selection of solvent system will be different, you can try some more solvent system) in practical work, and then add in tertiary Ding Jijia ether extraction, we found uncle Ding Jijia ether layer by TLC oxygen triphenyl phosphine and compound 3 ratio of 3:1, and hydrolysis of by-products, if with ethyl acetate is also unable to achieve the goal of effective separation, It indicates that the single solvent system cannot separate the product and triphenylphosphine well. We also attempted to extract the mixed solution of PE:EA (6:1). TLC was used to detect that the extraction solution contained only triphenylphosphine and no compound 3, indicating that the mixed system was an ideal combination. The mixed extract was repeatedly extracted for 4 times. The aqueous phase was reversely extracted with DCM, and then the organic phase was dried. After evaporation, compound 3 was obtained, with LCMS purity reaching 85%. From this case can promote method is, in view of the product of the larger, and it is oily matter exists, try a single or a different combination of mixed solvent (preferably) mixed solvent system, scatter triphenylphosphine and product to two different phase (product) into the water phase to the greatest extent, to achieve the purpose of separation. In the process of this attempt, combined with TLC to find the best combination and ratio, may take a little time, single often have the effect of the intention, let us solve the problem of triphenylphosphine difficult to produce.