Sciencemadness Discussion Board

Benzaldehyde

technologist - 5-12-2007 at 21:24

I am looking for a synthetic route (Of course commercially cheaper) to produce p-hydroxy Benzaldehyde.

May start from Banzaldehyde or Toluene

chemrox - 5-12-2007 at 21:49

Riemer-Tiemann reaction from phenol

smuv - 6-12-2007 at 10:05

@chemrox the Riemer-Tiemann reaction would give mostly an ortho product.

Technologist maybe you should look into anethole, which can be converted to p-methoxy-benzaldehyde. Although not exactly what you are asking for, but since it seems you are looking to make a 4-substituted phenylethylamine analogue, it maybe ok.

technologist - 6-12-2007 at 20:45

Dear SMUV
I think it will be easier if I go for addition of Aldehyde group to Phenol at para position compared to going for Hydroxy group in benzaldehyde.

What is your view. Actually looking for cheapest route for 4-hydroxy benzaldehyde.

Should start from any simple & cheaper molecule.

chemrox - 6-12-2007 at 23:09

@SMUV- that's right, the intermediate keto pulls e's from the pi bond adjacent so the product is ortho .. I wasn't thinking ..

and I was also thinking the fellow should do some reading on his own before asking everyone to do these for him. Once he's tried a few things and wants some help .. then he should ask.

smuv - 7-12-2007 at 07:17

Actually chemrox...you are kind of right. Last night I stumbled upon some Riemer-Tiemann formylation reactions where the ratio of para to ortho isomers was reversed. The article was written in Chinese so I was only able to view an abstract but apparently the presence of tertiary amines greatly changes the regioselectivity of this reaction.

Huaxue Xuebao, 46(2), 155-8; 1988
Quote:
Abstract

In the presence of a tertiary amine, phenols underwent an abnormal Reimer-Tiemann reaction, i.e., the ratio of the para- and ortho-products was reversed. For example, phenol gave 60% yield of p-hydroxybenzaldehyde, 7% yield of o-hydroxybenzaldehyde and 1% of tarry materials. Whereas in the absence of the tertiary amines, the yield of para-, ortho-, and tarry materials under the optimum conditions were 8-11, 38-45 and 20% resp. The conditions of the abnormal Reimer-Tiemann reaction were studied in detail and a mechanism was proposed. o-Methylphenol, and o-methoxyphenol underwent the above abnormal Reimer-Tiemann reaction similarly.


Edit another interesting one
Journal of Molecular Catalysis A: Chemical, 130(3), L205-L207; 1998
Quote:
In the presence of b-cyclodextrin and its derivatives, the photo-Reimer–Tiemann reaction of phenols with chloroform
proceeded smoothly with high selectivity for the formation of 4-hydroxy benzaldehydes.


The active ingredient in Febreze is cyclodextrin. The 3 isomers could easily be seperated by fractional crystallization as their solubilities in water vary greatly. In 50% MeOH w/ potassium carbonate as a base there is a 75% selectivity of the para product.

I will note however that the source of this research is a little iffy "Division of Tea Technology, UPASI Tea Research Institute, Valparai 642 127, India".



[Edited on 7-12-2007 by smuv]