Reimer-Tiemann reaction normal

The abnormal Reimer-Tiemann reaction involves a ring expansion, in the classical case from a pyrrole to a 3-chloropyridine, resulting from an attack of dichlorocarbene on a double bond. An electrochemical equivalent can be made by electrolysis in a chloroform solution, where the electrogenerated base produces dichlorocarbene. By using this method, 2,3-dimethylindole could be transformed to 3-chloro-2,4-dimethylquinoline in fair yield some of the normal Reimer-Tiemann product, 3-dichloromethyl-2,3-dimethyl-3//-indole, was also formed [164]. 

Castillo, R., Moliner, V., Andres, J. A theoretical study on the molecular mechanism for the normal Reimer-Tiemann reaction. Chem. Phys. Lett. 2000, 318, 270-275. 

Normally, however, we can expect the paraselectivity to be improved when the size of the cation is increased. The literature mentions at least three cases the Kolbe reaction (ref. 9), the Reimer-Tiemann reaction (ref. 10) and the hydroxymethylation of phenols in alcoholic media (ref. 11), where with hydroxide anion the para/ortho ratio is increased following the series of the cations Na+ < K+ < Cs+ < R4N+. ... 

The Reimer-Tiemann reaction, an aromatic substitution reaction that occurs under basic conditions, is in many respects a unique reaction. It is one of the few organic reactions whose industrial importance seems to increase yearly, notwithstanding the environmental hazards associated with the use of chloroform, while academic interest remains considerable. In addition to the fact that the normal reaction continues to intrigue chemists, the so-called abnormal Reimer-Tiemann reaction that furnishes substituted cyclohexadienes remains of considerable interest. Several previous surveys of the Reimer-Tiemann reaction have been published. Consequently, we focus here on recent developments. 

It is convenient to discuss the Reimer-Tiemann reaction in terms of its normal and abnormal versions. The normal reaction, discovered in 1876 by Reimer, consists of the treatment of a phenol or naphthol with chloroform in the presence of an alkali metal hydroxide solution (see equations 1 and 2), and results... 

Intriguing but confusing information is available in two Chemical Abstracts references to Chinese publications. A 1988 abstract d reports the behavior of phenol under Reimer-Tiemann reaction conditions with the addition of tertiary amines. The authors claim that the para. ortho ratio is reversed from that normally observed and 60% yield of p-hydroxybenzaldehyde, 7% yield of o-hydroxybenzaldehyde and only 1% tars are obtained when phenol is subjected to the new conditions. One year later a report appeared in which it is claimed that the use of tertiary amines under phase-transfer conditions increases the yield of ortho product. The authors report a yield of 79% of salicylaldehyde from phenol using 0.37% catalyst (the nature of the catalyst is not mentioned in the abstract and the Chinese publication is not available to this author), and 35% sodium hydroxide at 55-60 °C for 90 min. Surely, these results (or the translation) warrant checking. 

It is interesting to compare early experimental work with the facilities available in a modem laboratory. Von Auwers was the first to separate the chloro ketones from the normal phenolic aldehydes of the Reimer-Tiemann reaction. Identirication and strocture proof by chemical means followed. It is a tribute to von Auwers skill and insight that his identification procedures have withstood the onslaught of modem spectroscopic means. Although the chloro ketones (equations 8-10) have been called the abnormal products of the reaction, in cases where the ortho and para positions are occupied (see equation 10) only ketonic material is obtained.In fact, the presence of the dichloro ketones provides one of the better arguments for the intermediacy of dichlorocarbene in the reaction mechanism. ... 

As is the case with the normal reaction, the abnormal reaction can also be influenced by the use of 3-cyclodextrin to give higher selectivity for the para position. Australian chemists have carried out a careful product analysis of the normal, abnormal and ring-expansion products resulting from the Reimer-Tiemann reaction with a series of 4-alkylguaiacols. ... 

A theoretical study on the molecular mechanism for the normal Reimer-Tiemann reaction ... 

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