Hypophosphorous acid, reactions

The oxidations of hypophosphorous acid, reaction (1), and of phosphorous acid, reaction (2), have been studied . ... 

The replacement of 2-amino group by a hydrogen can be achieved by diazotization, followed by reduction with hypophosphorous acid (1-8, 13). Another method starting from 2-aminothiazole is to prepare the 2-halo-thiazole by the Sandmeyer reaction (prepared also from the 2-hydroxy-thiazole), which is then dehalogenated chemically or catalytically (1, 9, 10). 

Complexes of Ir(III) are kineticaHy inert and undergo octahedral substitution reactions slowly. The rate constant for aquation of prBr(NH3)3] " [35884-02-7] at 298 K has been measured at 2 x 10 ° (168). In many cases, addition of a catalytic reducing agent such as hypophosphorous acid... 

The fact that the element readily dissolves in aqueous media with disproportionation into PH3 and an oxoacid is immediately clear from the fact that P lies above the line joining PH3 and either H3PO2 (hypophosphorous acid), H3PO3 (phosphorous acid) or H3PO4 (orthophosphoric acid). Phe reaction is even... 

This reaction shows that the hydrated oxide SiCV-xHjO is acidic, since it reacts with a base-As we mentioned earlier, phosphorus can be found in four different oxidation states. The hydroxides of the +1, +3, and +5 states of phosphorus are hypophosphorous acid, H3P02, phosphorous acid, H3P03, and phosphoric acid, H3P04. Their structures are shown in Figure 20-4. As suggested by their names, these compounds are distinctly acidic, and are of moderate strength. The equilibrium constant for the first ionization of each acid is approximately 10-2 hypophosphorous acid ... 

The reaction is a sensitive one, but is subject to a number of interferences. The solution must be free from large amounts of lead, thallium (I), copper, tin, arsenic, antimony, gold, silver, platinum, and palladium, and from elements in sufficient quantity to colour the solution, e.g. nickel. Metals giving insoluble iodides must be absent, or present in amounts not yielding a precipitate. Substances which liberate iodine from potassium iodide interfere, for example iron(III) the latter should be reduced with sulphurous acid and the excess of gas boiled off, or by a 30 per cent solution of hypophosphorous acid. Chloride ion reduces the intensity of the bismuth colour. Separation of bismuth from copper can be effected by extraction of the bismuth as dithizonate by treatment in ammoniacal potassium cyanide solution with a 0.1 per cent solution of dithizone in chloroform if lead is present, shaking of the chloroform solution of lead and bismuth dithizonates with a buffer solution of pH 3.4 results in the lead alone passing into the aqueous phase. The bismuth complex is soluble in a pentan-l-ol-ethyl acetate mixture, and this fact can be utilised for the determination in the presence of coloured ions, such as nickel, cobalt, chromium, and uranium. 

Aldehydes and ketones added to hypophosphorous acid yield the corresponding hydroxy-substituted derivatives [79,169,170]. The reaction involving an aldehyde is shown in Eq. (99) ... 

Murphy et al. showed that EPHP [25] and L2P(0)H [26] can also be used in radical C-C bond forming reactions (Scheme 8). Recently, Piettre et al. [27] used the sodium salt of hypophosphorous acid as H-donor and the subsequent phosphonyl radical as phosphonylating agent for the preparation of 3-fura-nosyl-6 -furanosylphosphinate (Scheme 9). 

Scheme 11.6 gives some examples of the various substitution reactions of aryl diazonium ions. Entries 1 to 6 are examples of reductive dediazonization. Entry 1 is an older procedure that uses hydrogen abstraction from ethanol for reduction. Entry 2 involves reduction by hypophosphorous acid. Entry 3 illustrates use of copper catalysis in conjunction with hypophosphorous acid. Entries 4 and 5 are DMF-mediated reductions, with ferrous catalysis in the latter case. Entry 6 involves reduction by NaBH4. 

These authors also reported the synthesis of 1,2-oxaphosphole derivatives from the reaction of hypophosphoric acid with /Tun saturated aldehydes (Scheme 8)... 

The same report23 describes the generation of C-P bonds using red phosphorus under acidic conditions. The intermediate reactive species under these conditions is hypophosphorous acid.25 Using aqueous HI (57%) with dioxane, a 25% (purified) yield of benzylphos-phonic acid could be isolated from the reaction involving benzalde-hyde (Figure 2.8). Under the conditions of reaction, aqueous HI with... 

In the presence of an oxidant (Y), hypophosphorous acid (A) is transformed into phosphorous acid (B). The kinetics of the reaction has these features ... 

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. 

Reactions with thiono esters, iodides, bromides, and selenides proceed efficiently with dimethyl phosphite or with hypophosphorous acid in the presence of a tertiary amine and AIBN.221... 

Decant the solution and filter it with suction through a dense paper filte/ into a dry and clean Bunsen flask. Carefully evaporate the filtrate on a sand bath (in a fume cupboard ) until the temperature of the solution rises to 105-110 C (a thermometer ). See that the liquid does not boil and does not ignite. Cool the bowl in an ice and water mixture for 20-30 min. Filter off the crystals in a stream of nitrogen (see Fig. 64b) using a glass filter No. 2. Conduct reactions characterizing the properties of hypophosphorous acid. 

Amino- and 7-aminothiocoumarin have been thoroughly explored as useful precursors to a wide variety of thiocoumarins. Thus, substituents such as Cl, Br, I, SCN, CN, OH, and OMe have been introduced by way of the Sandmeyer reaction. 6-Aminothiocoumarin is brominated in the 5-posi-tion, whereby 5-bromo- or 5,6-dibromothiocoumarin may be made by way of the corresponding diazonium salt, using hypophosphorous acid or cuprous bromide, respectively. Alternatively, 6-acetylaminothiocoumarin may be nitrated in the 5-position and thus 5-nitro-, 5-amino-, 5,6-diamino-, or 6-chloro-5-nitrothiocoumarins can be prepared by classical syntheses. These derivatives are useful intermediates for the synthesis of further fused thiocoumarins (e.g., 23, 24 and 25 ). 

Diazotization has been reported for all the pyrazolopyridines, and in some cases the salts have been isolated. A 7-aminopyrazolo[4,3-c]pyridine (191a) was converted to the corresponding hydroxy compound with sodium nitrite in hot glacial acetic acid.159 Analogous products were obtained from a 3-aminopyrazolo[3,4-b]-15 and 2-aminopyrazolo[l,5-a]pyridine.186 Decomposition of diazonium salts with hydrobromic acid afforded 3-bromo-pyrazolo[3,4-c]-u0 or -[4,3-bjpyridines111 deamination of 3-aminopyra-zolo[3,4-h]pyridines was achieved via treatment of the diazonium salts with hypophosphorous acid,10 titanous chloride,238 or ferrous ammonium sulfate.238 Kocevar et al.236 have made a detailed study of the reactions of the latter diazonium salt. 

The solution of l,2 5,6-di-0-isopropylidene-ct-D-glucofuranose-3-0-(4-fluorophenyl)-thionocarbonate [Eq. (12)] 32 (83 mg, 0.2 mmol), hypophosphorous acid (0.1 mL, 1 mmol), and triethylamine (0.154 mL, 1.1 mmol) in dioxane (1.5 mL) under argon was treated with AIBN (6.5 mg) twice at 20 min intervals and under reflux. After completion, the reaction was washed with water and dried over anhydrous MgS04. After evaporation of the solvent, the residue was analyzed by H NMR to give 100% of the deoxy product 30. 

Complexes of (( Ir(III) are kinetically inert and undergo octahedral substitution reactions slowly. The rate constant for aquation of [IrBr(NH3)5]2+ [35884-02-7] at 298 K has been measured at -2 x 10-10 s-1 (168). In many cases, addition of a catalytic reducing agent such as hypophosphorous acid greatly accelerates the rate of substitution via a transient, labile Ir(H) species (169). Optical isomers can frequently be resolved, as is the case of ot-[IrCl2(en)2]+ [15444-47-0] (170). Ir(III) amine complexes are photoactive and undeigo rapid photosubstitution reactions (171). Other iridium complexes... 

Calcium Hypophosphite. CAS 7789-79-9, CalHiPOi) . white solid, snluhilily 15.4 g/100 g HiO at 2VC, formed (I) bv (toiling calcium hydroxide suspension in water and yellow phosphorus, (2) by reaction of calcium carbonate or hydroxide and hypophosphorous acid. 

Hypophosphoric acid is formed by reaction (I) of yellow phosphorous and potassium permanganate in sodium hydroxide medium. (2) of red phosphorus and calcium hypochlorite solution, (3) also one of the products of slow oxidation at ordinary temperatures of phosphorus in moist air. 

Hypophosphite. Sodium hypophosphite. [CAS 7681-53-0], NaH2P02 H20. white solid, soluble, formed (1) by reaction of hypophosphorous acid and sodium carbonate solution, and then evaporating, (2) by reaction of NaOH solution and phosphorous on heating (poisonous phosphine gas evolved). 

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