Fischer process

Phenylhydrazine condenses with acetoacetic ester to give a pyrazolone derivative which on methylation gives phenazone. The sulphonic acid similarly gives rise to the tartrazine dyestuffs. It is used to make indole derivatives by the Fischer process. 

Aminosugars such as glucosamine may be synthesized by a modified Kiliani-Fischer process (see Box 12.1). The starting aldose, here o-arabinose, is treated with ammonia, producing an imine, and then with HCN to yield epimeric 2-aminonitriles. The... 

Five years later, the same authors reported an improved total synthesis of arcyriaflavin A (345) starting from the TBS enol ether 1490 (for the synthesis see Scheme 5.252). This route involves two indolizations based on silyl enol ether nucleophilic attack and Fischer processes. Using Cadogan s procedure by heating in triethyl phosphite, the TBS enol ether 1490 was transformed into the ketone ( + )-1495, involving silyl enol ether-mediated indolization. Finally, Fischer indolization of (+ )-1495 by reacting with phenylhydrazine (524) led directly to arcyriaflavin A (345) in 57% yield (794) (Scheme 5.253). 

In the formation of glycosides by the Fischer process (equilibration in the presence of an acid catalyst), fucopyranosides are apparently formed more rapidly than galactopyranosides. In the presence of mineral acids, fucose attains equilibrium in boiling methanol within 6-8 h, whereas a reaction time of 20 h is customary for D-galactose. In reactions catalyzed by cation-exchange resins, maximum pyranoside formation is attained by 8 h for L-fucose,35a whereas D-galactose requires35612-24 h. 

In another variant, A-Boc-hydrazine (i-BuOCONHNH2) is coupled with an aryl halide via the carbamate nitrogen the subsequent Fischer sequence can be conducted in the same pot after addition of acid, with loss of the Boc group. ° Hydroamination of alkynes via various protocols ° also produces arylhydrazones, ready for the Fischer process. 

An exceptionally nsefnl adaptation is the Grandberg synthesis of tryptamines from 4-halo-butanals, or more often in practice their acetals, in which the nitrogen nsnally lost dnring the Fischer process is incorporated as the nitrogen of the aminoethyl side-chain. 

Synthesis with fluidized catalysts. Investigations made in the United States during the last decade (61) showed that the Fischer process could economically produce gasoline in this country if the necessary carbon monoxide-hydrogen mixture was produced from natural gas. New methods, however, seemed necessary for the commercial application... 

Ministry of Fuel and Power, Report on the Petroleum and Synthetic Oil Industry of Germany (London, 1947), 82-90 Germany s Home Production of Motor Fuels, Gas World 104 (9 May 1936) 421 Franz Fischer, The Conversion of Coal into Liquid Fuels, Chemical Age, 35 (24 Octoher 1936) 353-355 The Fischer Process, Chemical Age, 35 (31 October 1936) 367. 

Therefore, it was clear (Figure 11.5) that one of the two aldopentoses that gave rise to the dicarboxylic acids that retained optical activity had to be arabinose. Furthermore, when the Kiliani-Fischer process (Scheme 11.14, vide supra) was undertaken on both of those aldopentoses, only one of them gave hexoses that produced two six-membered aldaric acids, both of which were chiral. It was known... 

The differences between the individual iron-cyanide complex processes stem from the type of complex selected and the method of regeneration. In two processes, that of the Gesellschaft fur Kohlentechnik and the Fischer process, alkaline aqueous solutions of potassium ferricyanide and ferrocyanide are used, and regeneration is carried out by contact with air and electrolysis, respectively. The other two processes of this category, the Staatsmijnen-Otto and the Autopurification processes, employ suspensions of complexed ferric-ferro-cyanide compounds in alkaline solutions that are regenerated by air contact. The latter two processes are essentially identical, although they were developed independently in 1945 in the Netherlands and in England, respectively. 

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