Tollens’ reagents

Tollens reagent An ammoniacal solution of silver oxide which is used as a lest for aldehydes, which, unlike ketones, cause the deposition of a silver mirror. 

I Oxidation of a primary alcohol or an aldehyde yields a carboxylic acid (Sections 17.7 and 19.3). Primary alcohols are often oxidized with C1O3 in aqueous acid, and aldehydes are oxidized with either acidic Cr03 or basic silver oxide (Tollens reagent). 

D-Mannose reacts with acetone to give a diisopropylidene derivative (Problem 25.61) that is still reducing toward Tollens reagent. Propose a likely structure tor this derivative. 

Thymine, electrostatic potential map of, 1104 structure of, 1101 Thyroxine, biosynthesis of, 551 structure of. 1020 TIme-of-flight (TOP) mass spectrometry, 417-418 Titration curve, alanine, 1023 TMS, see Tetramethylsilane see Trimethylsilyl ether Tollens reagent, 701 Tollens test, 992... 

To identify the specific aldehyde that is actually involved in the light-emitting reaction of living luminous bacteria, Shimomura et al. (1974a) extracted and purified the aldehyde from 40 g each of the bacterial cells of P. phosphoreum, Achromobacter (Vibrio or Photobacterium) fischeri, and an aldehydeless mutant of A. fischeri. The aldehyde fractions were purified, and then oxidized with Tollens reagent (silver oxide dissolved in ammonia) to convert the CHO group into the COOH group. Then the acids obtained were analyzed by mass spectrometry. The results indicated that P. phosphoreum had contained a mixture of aldehydes dodecanal (5%), tetradecanal (63%) and hexadecanal (30%), as shown in Table 2.2. Thus, tetradecanal was clearly predominant in... 

Dichromate oxidation of secondary alcohols produces ketones in good yield, with little additional oxidation. For example, CH,CH2CH(OH)CH3 can be oxidized to CH CH2COCH3. The difference between the ease of oxidation of aldehydes and that of ketones is used to distinguish them. Aldehydes can reduce silver ions to form a silver mirror—a coating of silver on test-tube walls—with Tollens reagent, a solution of Ag1" ions in aqueous ammonia (Fig. 19.3) ... 

Aldehydes CH3CH2CHO + Ag+ (in Tollens reagent) gives CH3CH2COOH... 

FIGURE 19.3 An aldehyde (left) produces a silver mirror with Tollens reagent, but a ketone (right) does not. 

See Silver nitride, also Ammonia Silver compounds See also silvering solutions, tollens reagent... 

See FULMINATING METALS, SILVER-CONTAINING EXPLOSIVES, TOLLENS REAGENT... 

Since (B) does not reduce Tollens reagent, (B) is not an aldehyde, but must be a ketone. The only ketone with 4 Cs is CHjCOCHjCH, and (A) is CHjCCljCHjCH,. 

Tollens reagent, AgCNHjlj , is a specific oxidant for CHO->COOH. 

Problem 22.14 Glycosides do not react with either Fehling s or Tollens reagents and do not mutarotate. Explain. M... 

Tollens reagent, which is based on Ag(NH3)2, can be used to test for the presence of aldehydes. The weakly oxidizing system converts aldehydes to carbbkylates and if the reaction is slow and the walls of the vessel are clean, then a silver mirror can often be observed, otherwise a grey or black precipitate results. No oxidation of ketones occurs, except with or-hydroxy ketones, and on the basis of its reaction with sugars, they can be categorized as... 

Treat each with Tollens reagent Only pentanal will give a silver mirror. 

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