Hoesch

Hoesch synthesis A variation of the Gattermann synthesis of hydroxy-aldehydes, this reaction has been widely applied to the synthesis of anthocyanidins. It consists of the condensation of polyhydric phenols with nitriles by the action of hydrochloric acid (with or without ZnCl2 as a catalyst). This gives an iminehydrochloride which on hydrolysis with water gives the hydroxy-ketone. 

The Hoesch Reaction is employed for the introduction of the - COR group into the aromatic ring of phenol or a phenolic ether, and usually proceeds particularly readily with polyhydric phenols. If an ethereal solution of resorcinol (I)... 

To meet the needs of the advanced students, preparations have now been included to illustrate, for example, reduction by lithium aluminium hydride and by the Meerwein-Ponndorf-Verley method, oxidation by selenium dioxide and by periodate, the Michael, Hoesch, Leuckart and Doebner-Miller Reactions, the Knorr pyrrole and the Hantzsch collidine syntheses, various Free Radical reactions, the Pinacol-Pinacolone, Beckmann and Arbusov Rearrangements, and the Bart and the Meyer Reactions, together with many others. 

By the condensation of a nitrile with a phenol or phenol ether in the presence of zinc chloride and hydrogen chloride a hydroxyaryl- or alkoxyaryl-ketone is produced. The procedure is termed the Hoesch reaction and is clearly an extension of the Gattermann aldehyde reaction (Section IV,121). The reaction gives the best results with polyhydric phenols and their ethers with simple monohydric phenols the imino ester hydrochloride is frequently the sole product for example ... 

Haworth reaction Hell-Volhard-Zelinsky reaction Hoesch reaction Hofmaim reaction. ... 

To explain the experimentally observed high reactivity of HCN and alkyl nitriles under snperacidic condition, Shndo found that in the Gat-terman and Houben-Hoesch reactions, diprotonated HCN (or nitriles) are involved as the de facto reagents (HC N H2, RC N H2). 

Friedel-Crafts acylation using nittiles (other than HCN) and HCI is an extension of the Gattermann reaction, and is called the Houben-Hoesch reaction (120—122). These reactions give ketones and are usually appHcable to only activated aromatics, such as phenols and phenoHc ethers. The protonated nittile, ie, the nitrilium ion, acts as the electrophilic species in these reactions. Nonactivated ben2ene can also be acylated with the nittiles under superacidic conditions 95% trifluoromethanesulfonic acid containing 5% SbF (Hg > —18) (119). A dicationic diprotonated nittile intermediate was suggested for these reactions, based on the fact that the reactions do not proceed under less acidic conditions. The significance of dicationic superelectrophiles in Friedel-Crafts reactions has been discussed (123,124). 

HOUBEN - HOESCH Phenol Acylation Synthesis ol ketones (or aldehydes) by acylation ol phenols with nitriles (or ortho formates)... 

The methoxy group of methoxythiophenes shows a reactivity which, in many respects, differs appreciably from the reactivity of the corresponding anisoles. Thus, in an attempted Hoesch synthesis with 5-methoxy-2-thenylcyanide (167) and phloroglucinol, the methoxy group reacted instead and 5-(2, 4, 6 -trihydroxyphenyl)-2-thenyl cyanide (168) was obtained. 2-Thenyl cyanide reacts normally in the Hoesch synthesis, Likewise, upon acid hydrolysis of the reaction product of 5-methoxy-2-thienyllithium with benzophenone, (169) was obtained instead of the expected substituted methoxythiophene. No defined products could be isolated from the attempted Claisen rear-... 

An analogous reaction is the Houben-Hoesch reaction,(sometimes called the Hoesch reaction) using nitriles 7 to give aryl ketones 8. This reaction also is catalyzed by Lewis acids often zinc chloride or aluminum chloride is used. The Houben-Hoesch reaction is limited to phenols—e.g. resorcinol 6—phenolic ethers and certain electron-rich aromatic heterocycles ... 

The synthetic importance of the Houben-Hoesch reaction is even more limited by the fact that aryl ketones are also available by application of the Friedel-Crafts acylation reaction. 

Paeonol has been prepared synthetically by Hoesch he allowed 5 parts of resorcinmethyl ether to react with 3 parts of acetonitrile, with zinc chloride and ether. Chlorine was then passed through the mixture for four hours. The mixture was shaken with ether, and the aqueous solution steam distilled, when paeonol comes over with the steam, leaving the non-volatile isopaeonol in the flask. 

Friedel-Crafts acylation with nitriles and HCl is called the Hoesch or the Houben-... 

Hoesch reaction. In most cases, a Lewis acid is necessary zinc chloride is the most common. The reaction is generally useful only with phenols, phenolic ethers, and some reactive heterocyclic compounds (e.g., pyrrole), but it can be extended to aromatic amines by the use of BCls. Acylation in the case of amines is regioselectively ortho. Monohydric phenols, however, generally do not give ketones " but are attacked at the oxygen to produce imino esters. Many nitriles... 

Acylation of aromatic rings with nitriles (Hoesch)... 

German medium Precipitated Co Fixed bed 1939 Hoesch, Germany... 

Bertrand Thiel A variation of the Basic Open Hearth steelmaking process, suitable for ores rich in silicon and phosphorus. Two hearths are used by varying the quantities of hme added to each it is possible to concentrate most of the silicon and phosphoms in the slag from the first. Developed by E. Bertrand and O. Thiel at Kladno, Bohemia, in 1894 subsequently adopted at Hoesch, Germany (hence the alternative name for the process). 

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