Carboxylic acids => aldehydes

Reaction of carboxylic acids, aldehydes or ketones with hydrazoic acid... 

The reaction of carboxylic acids, aldehydes or ketones with hydrazoic acid in the presence of a strong acid is known as the Schmidt reaction A common application is the conversion of a carboxylic acid 1 into an amine 2 with concomitant chain degradation by one carbon atom. The reaction of hydrazoic acid with a ketone 3 does not lead to chain degradation, but rather to formation of an amide 4 by formal insertion of an NH-group. 

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. 

Conjugation chemistry for the coupling of haptens to carrier molecules is fairly well defined for compounds having common functional groups to facilitate such attachment. The types of functional groups generally useful for this operation include easily reactive components such as primary amines, carboxylic acids, aldehydes, or sulfhydryls. 

Transformation of Pseudoephedrine Amides into Highly Enantiomerically Enriched Carboxylic Acids, Aldehydes, Alcohols, and Ketones. 

Carboxylic acid, aldehyde, ketone, ether, alcohol, ester, ester-R (the chain attached to the oxygen atom being a generic substituent), anhydride, acetal, amide, epoxide, acid halyde, primary amine, primary imine, cyano, secondary amine, secondary imine, tertiary amine, nitro derivative, metal-1, metal-2, carbene, halo derivative. 

Peters R, Hellenbrand J, Mengerink Y, Wal Van der S. 2004. On-line determination of carboxylic acids, aldehydes and ketones by high-performance liquid chromatography-diode array detection-atmospheric pressure chemical ionization mass spectrometry after derivatization with 2-nitrophenylhydrazine. J Chromatogr A 1031 35. 

To summarize the amides are most suitable for the formation, by ortholithiation, of condensed heterocycles and polycyclic aromatics (in which subsequent rings are formed by intramolecular attack on the amide group). In other cases the removal of the amide group may be problematic, though if carboxylic acids, aldehydes or hydroxymethyl-substituted compounds are required, alternative amide substituents may be used. 

Symmetrical ethers are obtained from the dehydration of two molecules of alcohol with H2SO4 (see Section 5.5.3). Alcohols react with p-toluenesul-phonyl chloride (tosyl chloride, TsCl), also commonly known as sulphonyl chloride, in pyridine or EtsN to yield alkyl tosylates (see Section 5.5.3). Carboxylic acids, aldehydes and ketones are prepared by the oxidation of 1° and 2° alcohols (see Sections 5.7.9 and 5.7.10). Tertiary alcohols cannot undergo oxidation, because they have no hydrogen atoms attached to the oxygen bearing carbon atom. 

The materials were tested as supports for SPE techniques. Excellent recoveries are observed, exceeding silica-based SPE materials (40). The supports were also investigated for their retention behavior for phenols, alcohols, carboxylic acids, aldehydes, ketones, esters, chloroalkenes, and polycyclic aromatic hydrocarbons (41). 

Singlet excited state acid dissociation constants pK can be smaller or greater than the ground state constant pK by as much as 8 units. Phenols, thiols and aromatic amines are stronger acids upon excitation, whereas carboxylic acids, aldehydes and ketones with lowest >(71, ) states become much more basic. Triplet state constants pKr are closer to those for the ground state. Forster s cycle may be used to determine A pK =pK —pK) from fluorescence measurements if proton transfer occurs within the lifetime of the excited molecule. 

SAMPLE SOLUTION (a) The reactant is a primary alcohol and so can be oxidized either to an aldehyde or to a carboxylic acid. Aldehydes are the major products only when the oxidation is carried out in anhydrous media. Carboxylic acids are formed when water is present. The reaction shown produced 4-chlorobutanoic acid in 56% yield. 

SCHMIDT REACTION. Acid catalyzed addition of hydrazonic acid to carboxylic acids, aldehydes, and ketones to give amines, nitriles, and amides, respectively. 

The carboxyl function does absorb ultraviolet radiation, but the wavelengths at which this occurs are appreciably shorter than for carbonyl compounds such as aldehydes and ketones, and, in fact, are out of the range of most commercial ultraviolet spectrometers. Some idea of how the hydroxyl substituent modifies the absorption properties of the carbonyl group in carboxylic acids can be seen from Table 18-2, in which are listed the wavelengths of maximum light absorption (Amax) and the extinction coefficients at maximum absorption (emax) of several carboxylic acids, aldehydes, and ketones. 

Wavelengths tor Maximum Ultraviolet Absorption of Some Carboxylic Acids, Aldehydes, and Ketones (n--- n )... 

Excluding carboxylic acids, aldehydes, and ketones (see appropriate sections). b Other isomers were formed, but were not isolated. 

Detector will have response to ionizable compounds such as aromatics and unsaturated organics, some carboxylic acids, aldehydes, esters, ketones, silanes, iodo- and bromoalkanes, alkylamines and amides, and some thiocyanates... 

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