Triphenylphosphine reducing agent

The hberated iodine, as the complex triiodide ion, may be titrated with standard thiosulfate solution. A general iodometric assay method for organic peroxides has been pubUshed (253). Some peroxyesters may be determined by ferric ion-catalyzed iodometric analysis or by cupric ion catalysis. The latter has become an ASTM Standard procedure (254). Other reducing agents are ferrous, titanous, chromous, staimous, and arsenite ions triphenylphosphine diphenyl sulfide and triphenjiarsine (255,256). 

The ability of triphenylphosphine to act as a reducing agent probably involves initial formation of Ph3PCl2, which then undergoes solvolysis. If the synthesis is carried out using a small volume of ethanol, an orange polymorph is formed [45]. 

Azoxy compounds can be obtained from nitro compounds with certain reducing agents, notably sodium arsenite, sodium ethoxide, NaTeH, NaBH4—PhTeTePh, and glucose. The most probable mechanism with most reagents is that one molecule of nitro compound is reduced to a nitroso compound and another to a hydroxylamine 119-42), and these combine (12-51). The combination step is rapid compared to the reduction process. Nitroso compounds can be reduced to azoxy compounds with triethyl phosphite or triphenylphosphine or with an alkaline aqueous solution of an alcohol. ... 

For our unknown piperidine the other product is a penta-1,4-diene, the constitution of which can now identified by ozonolysis (in the presence of a reducing agent such as Zn dust, or triphenylphosphine, to prevent the oxidation of the ozonolysis fragments). Here ozonolysis will yield formaldehyde (methanal) (an indication that C-6 is unsubstituted) plus another aldehyde, XCHO (showing that C-2 bears the group X). The other product is a propanedial in which the groups Y and Z must occupy the central carbon. Clearly then, C-4 is substituted by both Y and Z. 

Sodium triacetoxyborohydride, 283 Other reducing agents Dichlorotris(triphenylphosphine)-ruthenium(II), 107 Dicyclopentadienyldihydrido-zirconium, 108 Samarium(II) iodide, 270 Sodium-Alcohol, 277 Tributyl tin hydride, 316 Reagents which can be used to reduce cyclic ketones to axial (less stable) alcohols... 

In certain cases reduction of NOf and NOf groups can be effected using carbon monoxide or triphenylphosphine. The reducing agent may first coordinate to the metal and then oxygen transfer can occur. Examples are shown in equations (13) and (14). 

Methods (i) and (ii) require palladium(II) salts as reactants. Either palladium acetate, palladium chloride or lithium tetrachloropalladate(II) usually are used. These salts may also be used as catalysts in method (iii) but need to be reduced in situ to become active. The reduction usually occurs spontaneously in reactions carried out at 100 °C but may be slow or inefficient at lower temperatures. In these cases, zero valent complexes such as bis(dibenzylideneacetone)palladium(0) or tetrakis(triphenylphos-phine)palladium(O) may be used, or a reducing agent such as sodium borohydride, formic acid or hydrazine may be added to reaction mixtures containing palladium(II) salts to initiate the reactions. Triarylphosphines are usually added to the palladium catalysts in method (iii), but not in methods (i) or (ii). Normally, 2 equiv. of triphenylphosphine, or better, tri-o-tolylphosphine, are added per mol of the palladium compound. Larger amounts may be necessary in reactions where palladium metal tends to precipitate prematurely from the reaction mixtures. Large concentrations of phosphines are to be avoided, however, since they usually inhibit the reactions. 

Common reducing agents are hydrogen in the presence of metallic or complex catalysts (e.g. Ni, Pd, Pt, Ru, Rh), hydrides (e.g. alanes, boranes, LiAlH4, NaBHJ, reducing metals (e.g. Li, Na, Mg, Ca, Zn), and low-valent compounds of nitrogen (e.g. NjH NjHJ, phosphorus (e.g. triethyl phosphite, triphenylphosphine), and sulfur (e.g. H0-CH2-S02Na = SFS, sodium dithionite = Na SjO. ... 

In the formation of the ylide from CBr4, two equivalents of triphenylphosphine are used. One equivalent forms the, ylidfe while the other acts as reducing agent and bromine scavenger. -... 

Dithiazolium cations can be readily reduced to the stable mono- and diradicals. Reaction of the disalt 43 could be effected, on a milligram scale, by electrolysis in an acetonitrile solution at 50 pA onto Pt wire cathode <1997JA2633>. Larger quantities could be obtained by chemical reduction. Attempts to reduce cation 43 directly with silver or zinc powder were unsuccessful. The most successful approach involved the use of triphenylantimony as reducing agent and bis(triphenylphosphine)iminium chloride ((PPN)Cl Equation (5)). The product obtained (7) is remarkably stable in the solid state, in air, and in organic solutions. 

As cyano-substituted ozonides were easily reduced by triphenylphosphine, also p-tolyl sulfide can be used as a reducing agent and the corresponding sulfoxide could be isolated in quantitative yield. Alternatively, the 3-cyano-3-phenyl-ozonide 103 can oxidize 2,3-dimethyl-2-butene to the corresponding epoxide (Scheme 34). 

Sodium azide, reaction with f-butyl chloroacetate, 45, 47 reaction with diazonium salt from o-amino-p -nitrobiphenyl, 46, 86 Sodium chlorodifluoroacetate, 47, SO reaction with triphenylphosphine and benzaldehyde, 47, SO Sodium ethoxide, 45, 25 reaction with diethyl succinate, 46,25 Sodium formate as reducing agent in preparation of palladium catalyst, 46,90... 

ArNOi — ArNHj.1 Na+[HFe(CO) ] is a known reducing agent in a basic medium. However, the bis(triphenylphosphine)imine (PPN) salt of HFe(CO)4 1 in combination with a strong Brpnsted acid (TFA) is also a reducing agent, particularly for nitroarenes, even in the presence of aldehydes or acid halides. 

Other reducing agents, such as hexakis[hydrido(triphenylphosphine)copper(I)] in benzene, H2/Pd-C in ethanol, lithium triethylborohydride in THF, failed to give the desired product. 

Reduction of acid chlorides to aldehydes One of the most useful synthetic transformations in organic synthesis is the conversion of an acid chloride to the corresponding aldehyde without over-reduction to the alcohol. Until recently, this type of selective reduction was difficult to accomplish and was most frequently effected by catalytic hydrogenation (the Rosenmund reduction section 6.4.1). However, in the past few years, several novel reducing agents have been developed to accomplish the desired transformation. Among the reagents that are available for the partial reduction of acyl chlorides to aldehydes are bis(triphenylphosphine)cuprous borohydride , sodium or lithium tri-terf-butoxyaluminium hydride, complex copper cyanotrihydridoborate salts °, anionic iron carbonyl complexes and tri-n-butyltin hydride in the presence of tetrakis(triphenylphosphine)palladium(0). ... 

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