Schmidt advantages

A potential advantage of the Schmidt reaction is illustrated by the conversion of progesterone to the 17j5-acetylamino derivative, without affecting the A-ring. A 35 % yield is obtained when 1 mole of sodium azide in polyphos-phoric acid is used. With excess azide the A-ring is transformed into an a,jS-unsaturated lactam ... 

By application of the Schmidt reaction, the conversion of a carboxylic acid into an amine that has one carbon atom less than the carboxylic acid, can be achieved in one step. This may be of advantage when compared to the Curtius reaction or the Hofmann rearrangement, however the reaction conditions are more drastic. With long-chain, aliphatic carboxylic acids yields are generally good, while with aryl derivatives yields are often low. 

There are actually three reactions called by the name Schmidt reaction, involving the addition of hydrazoic acid to carboxylic acids, aldehydes and ketones, and alcohols and alkenes. The most common is the reaction with carboxylic acids, illustrated above.Sulfuric acid is the most common catalyst, but Lewis acids have also been used. Good results are obtained for aliphatic R, especially for long chains. When R is aryl, the yields are variable, being best for sterically hindered compounds like mesi-toic acid. This method has the advantage over 18-13 and 18-14 that it is just one laboratory step from the acid to the amine, but conditions are more drastic. Under the acid conditions employed, the isocyanate is virtually never isolated. 

Aube took advantage of an intramolecular Schmidt reaction of azide 129 to provide the fused ring heterocyclic lactam 130 as a key step in a total synthesis of (+)-aspidospermidine... 

In addition, oligomers of other monosaccharides, such as arabinofuranose [429], galactofuranose [430,431] and xylose [432], were also synthesized efficiently by taking advantage of the Schmidt glycosylation procedure. 

Neumann, T., Junker, H. D., Schmidt, K., Sekul, R. (2007) SPR-based fragment screening advantages and applications. Curr Top Med Chem 7, 1630-1642. 

From our earliest example, we saw that it was advantageous to use dimensionless variables and that the characteristic quantities should be capable of being held constant. In addition, if a parametric study on the effect of varying some input quantity is to be performed, that quantity should appear in only the distinguished parameter. This is no restriction, for the others are proportional to powers of the distinguished parameter, and the proportionality constants are themselves dimensionless numbers. For example, if the viscosity is to be varied, the Reynolds and the Schmidt numbers are both functions of v, but ReSc is not so, if Sc is chosen as the dimensionless viscosity, Re = Cl Sc, where C = ReSc is independent of v. 

One of the advantages of GFAAS is the direct analysis of solid samples without prior decomposition, this technique has been reviewed by Bendicho and de Loos-Vollebregt (1991). The solid samples can be introduced directly or as a slurry. Calibration can be with aqueous standards, synthetic solids, standard additions or with SRMs. SRMs have been used for calibration for solid sampling of plant material (Schmidt and Falk, 1987). Examples of the use of solid samples with ETAAS are shown in Table 9-4. In many cases a matrix modifier is used with the sample, this allows the matrix to be volatilised at the pyrolysis stage without analyte loss, particularly important with volatile analytes such as Cd and Pb. (Ure, 1990). 

MgO nanoparticles have proven to be very effective chemical reagents in the Claisen-Schmidt condensation, which is a very valuable C—C bond-formation reaction commonly employed in the pharmaceutical and fine chemical industries [295]. When MgO(lll) nanosheets were employed for the Claisen-Schmidt condensation of benzaldehyde and acetophenone, they were found to exhibit activity superior to other systems, such as AICI3, BE3, POCI3, alumina and other reported nano-crystaUine MgO samples [296]. This development is particularly noteworthy as it represents a potential heterogenization of the Claisen-Schmidt catalytic process, which offers numerous advantages including easier product recovery and catalyst recycling. 

The use of supported platinum-based catalysts in hydrogen cyanide synthesis has been described, and some are in use in certain plants. For instance, Merrill and Perry recommended natural beryl coated with platinum or a platinum alloy [12], and a range of alternative supports were considered by Schmidt and his co-workers [13], including coated foamed ceramic and monolithic substrates. They are claimed to have some advantages in ammonia oxidation [14,15]. 

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