Sodium/ammonia

FIGURE 9 4 Mechanism of the sodium-ammonia reduc tion of an alkyne... 

Alkyne Sodium Ammonia Trans alkene Sodium amide ... 

The Beilby process started in 1891 and by 1899 accounted for half of the total European production of cyanide. In this process, a fused mixture of sodium and potassium carbonates reacts with ammonia ia the presence of carbon. In 1900, the Castner process, in which molten sodium, ammonia, and charcoal react to give a high (98%) grade sodium cyanide, superseded the Beilby process. Sodium cyanide became an article of commerce and soon replaced potassium cyanide in all except special uses. 

S-Benzyl and substituted S-benzyl derivatives, readily cleaved with sodium/ammonia, are the most frequently used thioethers. n-Alkyl thioethers are difficult to cleave and have not been used as protective groups. Alkoxymethyl or alkylthio-... 

Na, NH3, 97% yield. Sodium/ammonia is an efficient but nonselective reagent (RS-Ph, RS-CH2Ph, RS-CPh3, and RS-SR are also cleaved). 

Hg(OAc)2, H2O, 80% AcOH, HSCH2CH2SH, 25°, 5-20 min H2S, 2 h, high yield. The removal of an 5-benzylthiomethyl protective group from a dithioacetal with mercuiy(II) acetate avoids certain side reactions that occur when an 5-benzyl thioether is cleaved with sodium/ammonia. The dithioacetal is stable to hydrogen bromide/acetic acid used to cleave benzyl carbamates. 

Dithiols, like diols, have been protected as 5,5 -methylene, 5,5 -isopropylidene, and 5,5 -benzylidene derivatives, formed by reaction of the dithiol with formaldehyde, acetone, or benzaldehyde, respectively. The methylene and benzylidene derivatives are cleaved by reduction with sodium/ammonia. The isopropylidene and benzylidene derivatives are cleaved by mercury(II) chloride with sodium/ ammonia the isopropylidene derivative is converted to a monothio ether, HSCHR-CHRSCHMe2- ... 

The stereochemistry of the product resulting from the reaction of a 17-keto steroid with ethylidenetriphenylphosphorane is different from that of the 17-ethylidene steroids obtained by dehydration of 17a-ethyl-17/ -hydroxy compounds, Wolff-Kishner reduction of A -20-keto steroids or by sodium-alcohol or sodium-ammonia " reductions of 17-ethynyl carbinols. These latter products have generally been assumed to possess the trans configuration (C-21 methyl away from the bulk of the ring system) because of anticipated greater stability. The cis configuration for... 

Potassium hydroxide Cysteamine Carbon disulfide Dimethyl sulfate Sodium Ammonia Cyanamide Methylamine ... 

Benzylmercaptopropionyl-L-tyrosyl-L-phenyalanyl-L-glutaminyl-L-asparaginyl-S-benzyl-L-cysteinyl-L-prolyl-N-tosyl-D-arginyl glycinamide Sodium Ammonia Acetic acid... 

N-Carbobenzoxy-L-glutaminyl-L-asperaginyl-S-benzyl-L-cystainyl azide N-Carbobenzoxy-S-benzyl-L-cysteinyl-L-tyrosyl-L-phanylalanine azide Sodium Ammonia... 

I. Dauster, M. A. Suhm, U. Buck, and T. Zeuch, Experimental and theoretical study of the microsolvation of sodium atoms in methanol clusters Differences and similarities to sodium water and sodium ammonia. Phys. Chem. Chem. Phys. 10, 83 95 (2008). 

The stereochemistry of the photocycloadducts can be predicted from the result of a dissolving metal reduction of the same ,/)-unsaturated ketone. For example, sodium/ammonia reduction of 3,4-dimethylcydohexenone yielded trans- and cis-dimethylcyclohexanone 37 in a ratio of 84 16, which was similar to the ratio of the two photocycloadducts 38 (80 20) [33b, 42],... 

Carbenes add to the double bond of dihydropyrans, as they do to benzopyrans, to form cyclopropapyrans. For example, dichlorocarbene reacts with 2,3-dihydro-4//-pyran (593) to give the bicyclic pyran (618) which on heating at reduced pressure with quinoline undergoes ring expansion to the 3-chlorooxepine (620) the two chlorine atoms are removed by sodium-ammonia (60JA4085). The reaction of dihalocarbenes with pyrans and benzopyrans has been reviewed (630R(13)55). 

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