| Aromatic aldehydes range widely in nature, not only are they used widespreadly as organic intermediates in organic synthesis, but also they are important intermediate -s in the metabolic process of plants and animals. Therefore, they have a wide-ranging market prospect, there are many kinds of methods for synthesis of aromatic aldehydes, and the Sommelet reaction which is regarded as a important method was studied and applied.Sommelet reaction is an important and effective method for synthesis of aromatic aldehydes, close attention is paid to it because of its rawmaterials are low-cost and facile, the operation is simple, it has been widely used in the synthesis of aldehydes. traditional Sommelet reaction was reported like this: benzyl halides were treated with hexamethylenetetramine, with aqueous acetic acid as solvent, and whether the aldehydes were obtained or not depends on the value of pH of the solution, only when the value of pH was between 3～6, followed by hydrolysis to yield corresponding aromatic aldehydes. although many people has set out to explore and study the best conditions of synthesis of aldehydes utilizing traditional Sommelet reaction, However, this method suffered from one or more disadvantages. in order to overcome these disadvantageous results, this paper will study the improvement of the Sommelet method, compared with traditional method, the advantages of this method are as following:First, in the traditional Sommelet reaction, the yields were very low, it was inevitable that the side reactions would happen, such as Delepine reaction. and there were many complicated components, so it was difficult to isolate the target products form the system. However, it gave good yields and purity utilizing improved Sommelet reaction. For example, in the synthesis of 2,5-dimethyl-1,4-benzenedicarbo -xaldehyde, according to relevant repord, the best yield was 57%, while in the improved method, the yield rised to 85.8%.Second, some aromatic aldehydes could not be obtained or even though there were corresponding aldehydes resulted, the yield were very low, for example, the benzyl halides with a strongly electron-attracting group(CN, NO2 and so on); the larger steric hindrance compounds and poly-halomethylated benzyl halides, such as 2,4,6-tris(methyl)-1,3,5-benzenetricarboxaldehyde, and polyfluoro-substituted benzyl halides could hardly be obtained in traditional method, on the contrary, they were furnished in good yields and purity utilizing improved Sommelet method.Third, the reaction mechanism was not clearly stated in traditional method, in this paper, we come to see the reaction mechanism in a novel light. by adding solid amine sorbent in addition, using anhydrous system, improving temperature, all of these were advantageous to the synthesis of aldehydes. and it made the by-products which were producted in the Delepine reaction converted into corresponding aldehydes favorably.In the end, in order to simplify the operation, one-pot synthesis of corresponding aromatic aldehydes were tried, which got satisfying results.In the improved Sommelet reaction, we optimized every type of reaction condition, and in this way a series of aromatic aldehydes were synthesized, for example, some medicinal and industrial intermediates: p-nitrobenzaldehyde, 1,4-phthalaldehyde, 2,4-difluorobenzaldehyde, 2,5-difluorobenzaldehyde, 4,4'-biphen -yldicarboxaldehyde, and some larger steric hindrance compounds: 2,4-dimethyl-1,3,5-benzenetricarboxcarboxaldehyde, 2,4,6-tris(methyl)-1,3,5-benzene -tricarboxaldehyde, 2,4,6-tris(methyl)-1,3-benzenedicarboxaldehyde and so on, This is a facile procedure and easy to purify, and higher yield, so it is a excellent and efficient method. |
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