Stannous chloride, reaction with

Staggered conformation, 94 molecular model of, 94 Stannous chloride, reaction with nitroarenes, 928 Starch, 1—>4- -links in, 1000 structure of, 1000 Stationary phase, chromatography and, 432... 

The bimolecular reduction of aromatic nitro compounds, depending on reaction conditions, may produce azoxy compounds, azo compounds, hydrazo compounds (1,2-diarylhydrazines), benzidines, or amines. Whereas the reduction with zinc and sodium hydroxide leads to azo compounds, zinc and acetic acid/acetic anhydride produces azoxy compounds. Other reducing agents suggested are stannous chloride, magnesium with anhydrous methanol, a sodium-lead alloy in ethanol, thallium in ethanol, and sodium arsenite. 

The ammonium chloride does not figure in the equation for the reaction, but its volatilization serves to absorb excess of heat and prevents overheating of the sulfide. The latter decomposes at a temperature not much above that at which it is formed when no ammonium chloride is present. It may be that the latter lowers the temperature at which stannous chloride combines with sulfur, and it may have some other effect in producing good crystals. Its chief function, however, seems to be that of a heat absorber. Apparently, better results are obtained with precipitated stannous sulfide than with the purchased material. 

In most cases, the crude imino chloride is treated directly by adding it to a solution of stannous chloride saturated with dry hydrogen chloride the aldehyde is then liberated by steam distillation. The procedure is illustrated by the synthesis of o-tolualdehyde (70%). Imino chlorides have also been prepared by treatment of ketoximes with phosphorus penta-chloride, viz., RR C NOH — RCC1=NR, in preparations of benzalde-hyde and p-chlorobenzaldehyde (70-85%). As in the Stephen reaction (method 164), groups ortho to the imino chloride group hinder the reaction. 

A similar reaction occurs when an aqueous solution of a diazonium compound is made strongly alkaline and then warmed with an alkaline solution of stannous chloride. This reaction, however, involves the intermediate formation of the... 

From nitriles by treatment with anhydrous Stannous chloride dissolved in ether saturated with hydrogen chloride the resulting crystaUine aldimine stannichloride, [(RCH=NHj)2] SnCl, or (RCH=NH,HCl)2SnCl4, is hydrolysed by warm water, and the aldehyde is isolated by distillation with steam or by extraction with a solvent (Stephen reaction), for example, for R = CH3(CH2)4, i.e., n-amyl ... 

A sodium stannite solution was prepared by addition of aqueous sodium hydroxide (2.5 mol, lOOg) to aqueous stannous chloride (0.25 mol, 56g). The initially formed precipitate redissolved to form a clear solution. This solution was gradually added to a solution of 16.3g (0.1 mol) phenyl-2-nitropropene in THF at room temperature. A slightly exothermic reaction ensued, and the reaction mixture was stirred for 30 min, a saturated sodium chloride solution was added, and the solution was extracted with ether and the pooled extracts were evaporated under vacuum to give essentially pure P2P oxime in 80% yield. 

The Stephen s method allows the reduction of nitriles by stannous chloride in acid medium. If the amine chlorhydrate initially formed is hydrolyzed, the corresponding aldehyde is obtained (37, 91). Harington and Moggridge (37) have reduced 4-methyl-5-cyanothiazole by this method (Scheme 23). However, Robba and Le Guen (91) did not obtain the expected products with 4.5-dicyanothiazole and 2-methyl-4,5-dicyanothiazole. These compounds have been reduced with diisobutyl-aluminium hydride with very low yields (3 to 6%) (Scheme 24). In other conditions the reaction gives a thiazole nitrile aldehyde with the same yield as that of the dialdehyde. 

The other important direct alkylation processes involve reaction of electron-rich olefinic compounds with either tin metal or stannous chloride (tin(II) chloride) in the presence of stoichiometric amounts of hydrogen chloride (22). Butyl acrylate (R = C Hg) was used commercially in this process to prepare the estertin or P-carboalkoxyethyltin chlorides as iHustrated in the foUowing. 

The determination of tin in metals containing over 75 wt % tin (eg, ingot tin) requites a special procedure (17). A 5-g sample is dissolved in hydrochloric acid, reduced with nickel, and cooled in CO2. A calculated weight of pure potassium iodate (dried at 100°C) and an excess of potassium iodide (1 3) are dissolved in water and added to the reduced solution to oxidize 96—98 wt % of the stannous chloride present. The reaction is completed by titration with 0.1 Af KIO —KI solution to a blue color using starch as the indicator. 

Stannic and stannous chloride are best prepared by the reaction of chlorine with tin metal. Stannous salts are generally prepared by double decomposition reactions of stannous chloride, stannous oxide, or stannous hydroxide with the appropriate reagents. MetaUic stannates are prepared either by direct double decomposition or by fusion of stannic oxide with the desired metal hydroxide or carbonate. Approximately 80% of inorganic tin chemicals consumption is accounted for by tin chlorides and tin oxides. 

Anhydrous stannous chloride, a water-soluble white soHd, is the most economical source of stannous tin and is especially important in redox and plating reactions. Preparation of the anhydrous salt may be by direct reaction of chlorine and molten tin, heating tin in hydrogen chloride gas, or reducing stannic chloride solution with tin metal, followed by dehydration. It is soluble in a number of organic solvents (g/100 g solvent at 23°C) acetone 42.7, ethyl alcohol 54.4, methyl isobutyl carbinol 10.45, isopropyl alcohol 9.61, methyl ethyl ketone 9.43 isoamyl acetate 3.76, diethyl ether 0.49, and mineral spirits 0.03 it is insoluble in petroleum naphtha and xylene (2). 

Sta.nnous2-Ethylhexa.noa.te, Stannous 2-ethyIhexanoate, Sn(CgH 302)2 (sometimes referred to as stannous octanoate, mol wt 405.1, sp gr 1.26), is a clear, very light yellow, and somewhat viscous Hquid that is soluble in most organic solvents and in siHcone oils (166). It is prepared by the reaction of stannous chloride or oxide with 2-ethylhexanoic acid. 

Chlorate Analysis. Chlorate ion concentration is determined by reaction with a reducing agent. Ferrous sulfate is preferred for quaHty control (111), but other reagents, such as arsenious acid, stannous chloride, and potassium iodide, have also been used (112). When ferrous sulfate is used, a measured excess of the reagent is added to a strong hydrochloric acid solution of the chlorate for reduction, after which the excess ferrous sulfate is titrated with an oxidant, usually potassium permanganate or potassium dichromate. 

Catalysis is done by an acidic solution of the stabilized reaction product of stannous chloride and palladium chloride. Catalyst absorption is typically 1—5 p-g Pd per square centimeter. Other precious metals can be used, but they are not as cost-effective. The exact chemical identity of this catalyst has been a matter of considerable scientific interest (19—21,23). It seems to be a stabilized coUoid, co-deposited on the plastic with excess tin. The industry trends have been to use higher activity catalysts at lower concentrations and higher temperatures. Typical usage is 40—150 ppm of palladium at 60°C maximum, and a 30—60-fold or more excess of stannous chloride. Catalyst variations occasionally used include alkaline and non-noble metal catalysts. 

Reaction.—Make a solution of 4 grams stannous chloride in TO c.c. cone, hydrochloric acid, add 2 grams aminoazobenzene, and boil for a few minutes. On cooling ciystals of the hydrochlorides of aniline and yi-phenylenediamine separate out. The liquid is filtered and washed with a little cone, hydrochloric acid to remove the tin salts. If the precipitate is dissolved in water and made alkaline with caustic soda, a mixture of liquid aniline and solid/-phenylenediamine is precipitated, from which the former may be removed by filtering, washing, and draining on a porous plate. 

Azo- and Azoxy-compoiinds. Both classes of compounds ore usually highly coloured and are rapidly decolorised by v3rming with a solution of stannous chloride and hydrochloric acid, forming amino-cotnpounds (see Reactions, pp. i73i i77J-... 

Aniline 77 was converted into its diazonium salt with nitrous acid and this was followed by reduction with stannous chloride to afford the corresponding arylhydrazine 78. Condensation of 78 with 3-cyanopropanal dimethylacetal 79 gave the arylhydrazone 80. Treatment of 80 with PPE resulted in cyclization to indole 81. The nitrile group was then reduced to the primary amine by catalytic hydrogenation. Reaction of the amine with excess formalin and sodium borohydride resulted in Imitrex (82). 

Platinum, especially platinum oxide, has been used by many investigators (5), Platinum oxide, when used with aldehydes is apt to be deactivated before reduction is completed. Deactivation is inhibited by small amounts of ferrous or stannous chlorides (59,82). This type of promoter can also sharply curtail hydrogenolysis if it is a troublesome reaction (Rylander and Starrick, 1966). Deactivated systems can often be regenerated by shaking the reaction mixture with air (2,8,21 J3,96). The usefulness of this regenerative technique transcends aldehyde reductions it frequently is worth resorting to. 

B. Reduction of Dinitrodurene.—A solution of 90 g. of dini-trodurene in 1 1. of glacial acetic acid is boiled in a 12-I. flask (Note 6) 700 g. of stannous chloride is dissolved in 800 cc. of concentrated hydrochloric acid and heated to boiling. The heat is removed from the acetic acid solution of the nitro compound, and the stannous chloride solution is poured very carefully (during about ten minutes) into the dinitrodurene solution. The reaction is complete in fifteen minutes, and as the solution cools the stannic chloride compound of the diamine begins to crystallize. The reaction mixture is cooled to io° in an ice-water bath, and the solid is filtered off by suction, washed twice with 50 cc. of 95 per cent ethyl alcohol and twice with 50 cc. of ether, and dried. The filtrates from the tin compound contain very little of the reduction product and may be discarded. The composition of this compound is [G (CH i)4(NH2-HCI)2l2-SnCl4, and it crystallizes from the reaction mixture in fine, glistening plates which are almost colorless. The yield is 145 g. (97 per cent of the theoretical amount). 

The success of this type of reaction depends on the quality of the catalyst. The most active and dependable form of anhydrous stannous chloride 1 is prepared as follows In a 600-cc. beaker is placed 204 g. (189 cc., 2 moles) of acetic anhydride (99-100 per cent) and, while the liquid is stirred by hand, 226 g. (1 mole) of commercial c.p. crystalline stannous chloride dihydrate is added. This operation should be performed in a hood, for the heat of the reaction is sufficient to cause the acetic anhydride to boil. After about one and a half hours, the anhydrous stannous chloride is filtered on a large Buchner funnel, rinsed with two 50-cc. portions of dry ether, and dried overnight in a vacuum desiccator. The yield is quantitative (189 g.). The product may be kept in a tightly closed bottle until it is wanted. The product secured by dehydrating crystalline stannous chloride in an oil bath at 195-200° is satisfactory in many instances but is not dependable. 

This analytical procedure is based on an optimum analysis condition for segmented continuous flow analysis. The sample is combined with a molybdate solution at a pH between 1.4 and 1.8 to form the //-molybdosilicic acid. After an appropriate time for reaction, a solution of oxalic acid is added, which transforms the excess molybdate to a non-reducible form. The oxalic acid also suppresses the interference from phosphate by decomposing phosphomolyb-dic acid. Finally, a reductant is added to form molybdenum blue. Both ascorbic acid and stannous chloride were tested as reductants. 

Dinitro-1,5-benzenediol was then reduced with stannous chloride in concentrated hydrochloric acid at 50-60°C. At the beginning, the solution was clear, then some white crystals precipitated form the reaction solution. After cooling, the resultant precipitate was collected by filtration and washed with cold water to give 2,4-diao ino-l,5-benzenediol dihydrochloride-no mp. before it decomposed above 2C0°C. 

---