Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B17/00—Sulfur; Compounds thereof
  • C01B17/64—Thiosulfates; Dithionites; Polythionates
  • C01B17/66—Dithionites or hydrosulfites (S2O42-)

Definitions

• This invention relates to the making of alkali metal hydrosulfites, and particularly relates to a new and improved method for making anhydrous sodium hydrosulfite, a reducing material Widely used in the bleaching of textiles and of ground wood pulp for newsprint.
• both the sodium amalgam and the electrolytic reduction of bisulfites have resulted in relatively poor overall yields in the anhydrous hydrosulfite product. Both require the use of dilute aqueous solutions, and there is a natural tendency for the sodium hydrosulfite to decompose readily in the presence of Water or when in the dihydrate state.
• the electrolytic reduction procedure requires relatively complex and expensive equipment.
• an alkali metal formate reduction is utilized in a manner superficially similar to either of the foregoing patented processes, but the reaction is performed entirely in a water soluble organic solvent having a mildly active carbonyl, sulfinyl, or phosphoryl group.
• the carbonyl, sulfinyl, or phosphoryl group apparently act as a catalyst in promoting the conversion of bisulfites to hydrosulfites.
• the reason for this catalytic activity is not exactly understood, but the course of the reaction seems to indicate the temporary formation of bisulfite and hydrosulfite addition products.
• Suitable solvents which may be employed as the reaction medium in the present invention are: dimethyl formamide, dimethylacetamide, N-methylacetamide, die-thylacetamide, dimethyl sulfoxide, tetramethyl urea and hexamethyl phosphoramide.
• the preferred solvents for the reaction medium are dimethylfor-rnamide (DMF) and dimethylacetamide (DMAC), and I have found that in such a medium a very high quality anhydrous sodium hydrosulfite is produced-a yield of about 85 percent based on sulfur and 69 percent based on sodium formate. My process does not require any special reflux equipment nor is there any care required in the order of adding the reactants. The reaction is quite rapid, reaction time being one-third or less than any of the hitherto practiced commercial processes.
• the water content of the dimethylformamide reaction medium may be most conveniently in the range of to -35%.
• the DMF solvent mixture is relatively nonvolatile in comparison to the previously employed aqueous alcoholic environments.
• EXAMPLE I 50 grams of sulfur dioxide were first sparged into 500 ml. -('472 grams) of dimethylformamide placed in an 800 ml. beaker. 65 grams of reagent grade sodium formate and 74.5 grams of sodium metabisulfite (equivalent to 81.6 grams sodium bisulfite) were placed in a 1,000 ml. flat bottom distilling flask equipped with a glass tube trombone coil, a thermometer, and a magnetic stirrer. 200 ml. of hot water were added to the flask and the contents heated to 50 C. with stirring. At this stage, the dimethylformamide sulfur dioxide mixture was added from a separatory funnel with stirring of the flask and at such a rate that the addition was complete in about minutes.
• Example III The procedure of Example I is followed except that 150.5 grams of sulfur dioxide were dissolved in 500 mls. of dimethylformamide for addition to the reaction flask. 47.6 grams of sodium hydroxide and 95 grams of sodium formate were dissolved in 200 mls. of water in the reaction flask. The dimethylformamide solution was added to the flask over a minute period with the flask at 55 C. during the first half of the addition and 60 'C. during the second half. Following the dimethylformamide addition, the flask was stirred for an additional 70 minutes at 63 C. The crystals of sodium hydrosulfite were then filtered off, washed with 75 ml. of ethanol, and dried in a vacuum oven for one hour at 55 C. 182 grams of product analyzing 91.6% sodium hydrosulfite were obtained, providing a yield of 81.7% (100% hydrosulfite) based on sulfur.
• Example I the quantity of sulfur used in Example I was the same as in Example II, but was included as sulfur dioxide rather than as a mixture of bisulfite and sulfur dioxide.
• DMF-S0 mixture As the DMF-S0 mixture is added to the reactor a change in color to a tan or brown is noted. There also may be a blue streak in areas of high concentration of DMF-S0 These color manifestations are perfectly normal and indicative of the presence of S 0 and its polymerization products. However, a bright yellow color in dicates decomposition and the formation of elemental sulfur.
• the proportions of reactants to solvent given in the foregoing examples can be varied to considerable extent. It is quite feasible to use sodium metabisulfite, bisulflte, or sulfur dioxide and caustic soda. One may also employ sodium sulfite to balance off the greater amount of sodium ion introduced by an equivalent increase in sulfur dioxide absorbed in DMF.
• the various ratios of the reactants are not critical and some flexibility is permitted.
• Example 11 sets forth the use of 75 grams of sulfur dioxide per 500 ml. of DMF solvent. The reaction can be carried out and equivalent yields can be obtained with a mixture of ingredients such that the above ratio is reduced to 50 grams of sulfur dioxide per 500 ml. of DMF with a corresponding reduction of the other reactants (c.f. Example I).
• the DMF be absolutely anhydrous prior to introduction into the system for absorbing sulfur dioxide.
• the amount of water present be low at this stage since any water introduced into the system is more advantageously directed into the bisulfite-formate end of the process.
• the absorption of sulfur dioxide into DMF is accomplished extremely readily and the capacity for sulfur dioxide absorption is very high. There is negligible solvent loss.
• Kirk-Othmer, Encyclopedia of Chemical Technology, 2nd ed. vol. 19, page 420 states that the amount of sulfur dioxide capable of being absorbed inDMlfisz'.
• the optimum reaction temperature appears to be approximately 60 C. There is a tendency for the product 'to decompose at temperatures above 65 C. and the rate ofIeactiOn is decreased at lower temperatures. Accordingly, the use of 60 as an optimum temperature permits a couple of degrees swing either way with allowance for saftety and utility.
• the overall reaction is generally endothermic by calculation, about 4 kilocalories per mole of sodium hydrosulfite.
• heat is given otf during the first third of the reaction period. Following this first period, heat must be supplied to promote the reactions and boil off carbon dioxide. Therefore a combination cooling-heating coil is provided in the reactor.
• the bisulfite-formate-water mixture is first placed in the reactor, heated to about 50 C., and the DMF-sulfur dioxide component introduced with moderate stirring provided. While other sequences may be utilized, the yield may suffer somewhat as a result.
• the DMF addition should be, performed in about to minutes, and during this period heat evolution is the greatest and causing a temperature riseto about 60 C. Cooling is required during this period.
• the reactor is stirred moderately for about an additional one and one-quarter hour while the tempermine is maintained at 60 C. or slightly higher.
• the crystals formed by the subject process are very 'easilyfiltered although they have a particle size on the 'order of 40 microns (325 mesh). There is no delay in drainage on a Buchner filter and ordinary general purpose filter paper is satisfactory. Since dimethylformamide ha's a low ,vo latility, it is preferable to wash the hydrosulfite product free of this solvent prior to drying. Ap-
• Example V The ingredient formulation of Example II was repeated using N-methylacetamide as the reaction medium. 500 mls. of N-methylacetamide were used in conjunction with 200 mls. of water, and the procedure of Example I was again followed.
• EXAMPLE VI The reaction medium was formamide. Again, using the ingredient formulation of Example II and following the procedure of Example I, 500 mls. of formamide was utilized in conjunction with 200 mls. of water.
• Example VII The procedure of Example I was repeated, except that dimethyl sulfoxide was substituted for dimethyl formamide as the solvent reaction medium. An intense inky blue color, indicating the presence of disulfur trioxide was obtained. However, the color disappeared in about one hour leaw'ng a white salt.
• the sodium hydrosulfite product obtained from the reaction using DMSO as the reaction medium was slimy, and difiicult to filter and dry. The product was also somewhat unstable.
• the reaction is accelerated by the presence of water, as evidenced by the reduction in intensity of the blue or green color during the initial portion of the reaction when the water-DMSO ratio was increased.
• the maximum yield of the hydrosulfite product (based on sulfur) was about 61% and the purity was about 40%, such a yield having been produced when the DMSO-water proportion was approximately :20, and the reaction temperature was in the vicinity of 60 C.
• tetramethylurea is yet another solvent of the subject category which is useful as the reaction medium for making hydrosulfites.
• solubility problems may arise such that desirable catalytic effects may be offset by the physical conditions during reaction.
• Example VIII The procedure of Example I was repeated using tetramethyl urea (TMU) as the reaction medium. During the course of the reaction, the mixture became exceedingly thick, although the viscosity decreased as the reaction proceeded.
• TNU tetramethyl urea
• the yield of sodium hydrosulfite product using TMU as the reaction medium was 55.4 percent hydrosulfite) of a product assaying at 47.9 percent.
• dimethyl formamide and dimethylacetamide are the preferred reaction media since the reaction rate is slower and more easily controlled.
• the overall reaction rate with the latter two solvents is still three times faster than using either methanol or ethanol.
• the hydrosulfite product yield with DMF is superior than with alcohol being about 85% and 70% based on sulfur and formate respectively as compared to 70% and 38% respectively when alcohol is used.
• alkali metal hydrosulfite by reacting sulfur dioxide and an alkali metal formate with an alkali metal compound selected from the group consisting of alkali metal bisulfites, alkali metal metabisulfites, and alkali metal hydroxides, the improvement which comprises performing the reaction in a medium containing a solvent selected from the group consisting of dimethyl formamide and dimethylacetamide.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Low-Molecular Organic Synthesis Reactions Using Catalysts (AREA)

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Cited By (4)

• 1972
  • 1972-08-03 US US00277706A patent/US3826818A/en not_active Expired - Lifetime
  • 1972-10-17 JP JP47103289A patent/JPS4945898A/ja active Pending
  • 1972-11-14 SE SE14795/72A patent/SE369704B/xx unknown
  • 1972-11-22 IT IT54212/72A patent/IT974488B/it active
  • 1972-12-08 DE DE2260208A patent/DE2260208A1/de active Pending
  • 1972-12-18 CA CA159,197A patent/CA976725A/en not_active Expired
• 1973
  • 1973-01-10 GB GB135273A patent/GB1411185A/en not_active Expired
  • 1973-01-29 FR FR7303068A patent/FR2194644B1/fr not_active Expired

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