Hypophosphorus acid

Tiazofurine (142) is an antimetabolite with antineoplastic activity. It preferentially affects leukemic lymphocytes over normal cells due to selective activation by formation of its adenine dinucleotide by transformed cells. Of the syntheses available, one starts by conversion of iniidate 138 to methyl 2,5-anhydroallonothioate (139). Next, condensation with ethyl 2-amino-2-cyanoac-etate leads to the thioamide which undergoes thiol addition to the nitrile function to produce the amminothiazolecarboxyester system of 140 directly. Sodium nitrite in aqueous hypophosphorus acid eliminates the superfluous amino group via the diazonium transformation to give 141. This synthesis of tiazofurine (142) concludes by ester amide exchange in methanolic ammonia [48]. 

The Hypophosphorus Acid Deamination of Diazonium Salts in Deuterium... 

Table 10 Reaction of hypophosphorus acid with 4-amino-1,2,4-triazole derivatives (Equation 29)...

In addition, aryl triflates have proven to be viable substrates for the Pd-catalyzed Csp2—P bond formation reactions [87-90], Intriguingly, phosphorylation can be achieved from the Pd-catalyzed coupling of alkenyl triflate with not only dialkylphosphites, but also with hypophosphorous acid [88]. Thus, phosphinic acid 87 was obtained when triflate 86 was treated with hypophosphorus acid in the presence of Pd(Ph3P)4. Due to the abundance of alkenyl triflates and milder reaction conditions, alkenyl triflates have certain advantages over the corresponding alkenyl halides as substrates for Pd-catalyzed phosphorylations to make alkenyl phosphonates or phosphinates. 

Technical grade hydriodic acid is a 47% HI solution and usually has a brown color due to the presence of free iodine, produced by air oxidation of HI. Hydriodic acid should be stored in the dark to prevent photochemical decomposition, and free from air to prevent oxidation. The addition of 1.5% hypophosphorus acid (H3PO2) prevents oxidative decomposition. 

The phosphorus atom in hypophosphorus acid is in the lowest oxidation state, + 1. The compound is, therefore, a powerful reducing agent. It combines readily and often explosively with oxidizing agents. For example, the acid reduces mercury(II) nitrate or mercury(II) oxide into mercury metal violently. 

Hypophosphorus acid -m selenium analysis [SELENIUM AND SELENIUM COMPOUNDS] (Vol 21) - [PHOSPHORUS COMPOUNDS] (Vol 18)... 

An effective reagent is aqueous hypophosphorus acid, and an example of its use has been described in detail for the synthesis of 3,3 -dimethylbiphenyl from 4,4 -diamino-3,3 -dimethylbiphenyl (o-tolidine).30 As the latter compound is carcinogenic its preparation is ill-advised. More recently the deamination of diazonium salts with t-butyl nitrite in dimethylformamide has been shown to have wide applicability.31 The reaction proceeds smoothly at 65 °C with the evolution of nitrogen gas, the volume of which may be measured and used to monitor the reaction. The mechanism of the reaction is thought to involve the following radical sequence in which the solvent (DMF = solH), is the hydrogen donor. 

In most natural water, phosphine is very unstable and oxidizes even under anoxic conditions. Depending upon the redox potential of water, the oxidation products are diphosphine (P2H4), phosphorus, hypophosphorus acid, phosphorus acid, and phosphoric acid (Kumar et al. 1985). Based on soil studies (Berck and Gunther 1970 Hilton and Robison 1972), small amounts of phosphine may also be adsorbed (reversible sorption) or chemisorbed (irreversible sorption) to suspended solid and sediments in water. However, based on the estimated Henry s law constant (H) of 0.09 atm-m3/mol (see Table 3-3) and the expected volatility associated with various ranges of H, volatilization is expected to be the most important loss process for phosphine in water. 

Small Quantities. Wear goggles and protective gloves and clothing. Work in the fume hood. To 0.25 g of 2-acetylaminofluorene in a 50-mL round-bottom flask add 10 mL of concentrated hydrochloric acid. Fit the flask with a condenser and heat under reflux for at least 10 hours when all trace of yellow should have disappeared. Cool the contents of the flask to 0°C in an ice-salt bath and, over a period of 5 minutes, add dropwise a solution of 0.13 g of sodium nitrite in 0.3 mL of water. Stir the mixture for 30 minutes, then slowly add 2.7 mL of ice-cold 50% hypophosphorus acid. After stirring at room temperature for 16 hours, filter the mixture, wash the filtrate into the drain with water, and discard the solid (fluorene) with normal refuse or package and label for disposal by incineration.4-6... 

Amino-8-bromophenanthridone can be deaminated smoothly by the action of cold hypophosphorus acid on the diazonium chloride.122 1-Bromophenanthridone is formed in moderate overall yield from the amino compound when the diazonium bromide-mercuric bromide complex is heated at 120° and a number of bromo- and chloro-phen-anthridones have been obtained recently by Sandmeyer procedures.26, 101... 

Hypophosphorus acid, H3P02 in the presence of AIBN and a base (amine or NaHC03) can reduce organic halides and xanthates in dioxane or aqueous alcohols. Eq. 12.6a to 12.6d shows the reduction of xanthate, thionocarbonate, and iodoarene, and 5-exo-trig cyclization respectively [35-43]. 

Antioxidant Agent that inhibits oxidation and thus is used to prevent deterioration of preparations by oxidative process Ascorbic acid, ascorbyl palmitate, butylated hydroxyanisole, butylated hydroxytoluene, hypophosphorus acid, monothioglycerol, propyl gallate, sodium ascorbate, sodium bisulfite, sodium formaldehyde, sulfoxylate, sodium metabisulfite... 

The best general reagent for the reductive elimination of the diazonium group is hypophosphorus acid. Reduction proceeds readily at 0-5° with an aqueous solution of the reagent. The yields of hydrocarbons are in the range of 60-85%. Hydrochloric acid is recommended for the diazo-tization except in certain cases in which nuclear halogenation occurs as a side reaction when this acid is used. 

An alternative, more limited, route to (24) and its derivatives involves the 2-amino compound (326) which results from the reaction of aminoguanidine and the [3, l]benzoxazine (327 Scheme 49) (68CB2106). Diazotization of (326) and then hypophosphorus acid produces 2-substituted derivatives of (24) (70JOC3448). 

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