| dc.description.abstract | The present status of knowledge about the chemistry of sulphur oxyhalides and sulphur–nitrogen–fluorine compounds has been reviewed in the introductory chapter. With this background, the present investigations have been planned and outlined under the scope of the present work.
The solvents required for the present investigations have been purified by standard procedures. Some special reagents, like anhydrous hydrogen iodide, have been prepared by employing standard methods. A new method has been standardized for the preparation of tetrasulphur tetranitride, involving the reaction between sulphur monobromide and ammonia in carbon tetrachloride medium. This method has certain advantages over the conventional method in that it is a simpler procedure and can be employed even in a moderately equipped laboratory. The conventional method makes use of the reaction between sulphur chloride and ammonia in carbon tetrachloride medium.
A mixture containing hydriodic acid, hypophosphorous acid, and hydrochloric acid is found to reduce elemental sulphur and several sulphur compounds to hydrogen sulphide quantitatively. Based on this reaction, an analytical procedure has been standardized for the quantitative estimation of elemental sulphur and some sulphur compounds. It should be noted that even gaseous samples can be analyzed by this procedure. Standard methods are employed for the estimation of sulphur, nitrogen, fluorine, and chlorine present in various compounds prepared during the present work. Physical techniques like infrared spectroscopy, NMR spectroscopy, and X-ray powder diffraction have been used for the characterization of compounds.
The new method evolved and standardized for the preparation of sulphuryl chlorofluoride during the present investigations involves the fluorination of sulphuryl chloride by lead fluoride in acetonitrile medium. Unlike the earlier methods reported in literature for the preparation of sulphuryl chlorofluoride, the present method does not involve conditions like high temperatures and pressures. The chlorofluoride is free from sulphuryl fluoride. Sulphuryl chlorofluoride undergoes quantitative reduction by anhydrous hydrogen iodide both in the gas phase and in carbon tetrachloride medium. The sulphur present in the compound is reduced to hydrogen sulphide with the liberation of 8 moles of iodine per mole of the chlorofluoride taken, according to the equation:
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It may be of interest to point out that this is in contrast to the behaviour of sulphuryl fluoride towards hydrogen iodide. Sulphuryl fluoride is unaffected by anhydrous hydrogen iodide.
Lithium aluminium hydride in tetrahydrofuran and sodium borohydride in diglyme react with sulphuryl chlorofluoride, forming a solid complex containing metal sulphide, metal chloride, and metal fluoride, which on acidification liberates hydrogen sulphide quantitatively.
Sulphuryl chlorofluoride does not react with metals and metal oxides at room temperature. At elevated temperatures (250–350°C) it reacts with metals like copper, silver, zinc, and iron, forming the corresponding metal chlorides, fluorides, and sulphur dioxide. However, with lead it forms lead chlorofluoride and sulphur dioxide. With metal oxides, it forms metal chlorides, metal fluorides, and metal sulphates. Again, with lead dioxide, lead sulphate and lead chlorofluoride are formed with the evolution of oxygen. Sulphuryl fluoride is formed in all these reactions. The formation of sulphuryl fluoride is found to be catalyzed by some metals and metal oxides. It is interesting to note that sulphuryl chlorofluoride has no action on nickel and zinc oxide even at 400°C.
Sulphuryl fluoride has been prepared for the first time by the fluorination of sulphuryl chloride by potassium fluoride and potassium bifluoride (KHF?) in boiling acetonitrile. Both sulphuryl chlorofluoride and sulphuryl fluoride are formed during the fluorination. Traces of silicon tetrafluoride and hydrogen chloride are also observed to be evolved. The two sulphuryl halides are separated from each other by fractional distillation and then purified. Sulphuryl fluoride is freed from traces of silicon tetrafluoride and sulphuryl chlorofluoride by treatment with dilute hydriodic acid and potassium permanganate solutions. The issuing gas is dried by passing through phosphorus pentoxide. The yield of sulphuryl fluoride is approximately 25%. Other metallic fluorides like sodium fluoride are also found to react with sulphuryl chloride, giving sulphuryl fluoride, but the yield of the fluorinated product (SO?F?) is less compared to that obtained with potassium bifluoride.
Lithium aluminium hydride in tetrahydrofuran reduces sulphuryl fluoride. The solid complex formed, on acidification, liberates hydrogen sulphide quantitatively. However, sulphuryl fluoride is not reduced by anhydrous hydrogen iodide. The fluoride is reduced by sodium borohydride in diglyme only partially. Only 60–70% of the sulphur is recovered as hydrogen sulphide, on acidification of the solid complex formed during the reaction. It is expected that sulphur present in this compound (SO?F?) is not reduced to the sulphide stage. The solid complex formed probably contains metal–oxygen–sulphur bonded species.
Sulphuryl halides — sulphuryl chloride, sulphuryl chlorofluoride, and sulphuryl fluoride — behave in a similar way towards amines. With primary amines they form symmetrically substituted sulphamides. The reaction of these sulphuryl halides with tert-butylamine [(CH?)?C–NH?] and benzylamine (C?H?CH?NH?) may be represented by the equation:
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X = Y = Cl for SO?Cl?, R = (CH?)?C for tert-butylamine
X = Cl, Y = F for SO?ClF, R = C?H?CH? for benzylamine
X = Y = F for SO?F?
The compounds have been isolated and characterized.
The products of reaction of the sulphuryl halides with secondary amines depend on the relative amounts of the two reactants. Reaction of piperidine with these sulphuryl halides has been studied in detail. When the molar ratio of the amine to the sulphuryl halide is 1:2, piperidine N-sulphonyl halide is produced according to the equation:
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X = Y = Cl for SO?Cl?
X = Cl, Y = F for SO?ClF
X = Y = F for SO?F?
It is interesting to note that piperidine N-sulphonyl chloride is formed as the major product in the reaction between sulphuryl chlorofluoride and piperidine when the molar ratio is 1:2. This is attributed to the larger heat of formation of hydrogen fluoride compared to hydrogen chloride and subsequently the formation of the amine hydrofluoride. Piperidine N-sulphonyl fluoride has also been prepared by the fluorination of piperidine N-sulphonyl chloride by potassium bifluoride in acetonitrile medium, in the presence of pyridine. Pyridine acts as a catalyst. Both the N-sulphonyl halides react with diethylamine forming substituted sulphonamide. The compound isolated in this reaction has the formula C??H??NSO?N(C?H?)?.
With excess of piperidine, all the three sulphuryl halides form sulphopiperidide:
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X = Y = Cl for SO?Cl?
X = Cl, Y = F for SO?ClF
X = Y = F for SO?F?
Tertiary amines give rise to solid adducts of the general formula SO?XY·2B (where B = a tertiary amine) with sulphuryl chloride and sulphuryl chlorofluoride. Complexes of sulphuryl chlorofluoride with pyridine and quinoline have been prepared and characterized. Sulphuryl fluoride, on the other hand, reacts with pyridine extremely slowly, taking several days to form a few milligrams of the complex. This comparative inertness of sulphuryl fluoride may be attributed to the closely surrounded and strongly bonded oxygen and fluorine atoms making nucleophilic attack on sulphur difficult.
In an attempt to prepare thionyl chlorofluoride by the fluorination of thionyl chloride by lead fluoride in acetonitrile medium, Similarly, sulphur dioxide and thionyl chloride are found to undergo fluorination at low temperatures (–60?°C and 50?°C respectively) to give sulphuryl fluoride and thionyl fluoride. It should be noted that sulphuryl chloride does not undergo fluorination by elemental fluorine even at room temperature.
While carrying out investigations on fluorination using elemental fluorine, it became necessary to have an indigenous source of elemental fluorine, as fluorine cylinders are not available in this country. It is also not easy to import elemental fluorine in cylinders from industrially advanced countries owing to restrictions imposed by the home governments.
A fluorine cell has been fabricated and commissioned for the laboratory-scale production of elemental fluorine. The design of the cell is similar to the one used by Cady et al. (vide Chapter VIII). This medium-temperature type cell operates at 80?°C. A nickel rod acts as the anode, and the cathode is made of mild steel. The composition of the electrolyte corresponds approximately to KF·2HF.
Elemental fluorine has been liberated at the rate of up to 2.5 litres/hour at 9 volts. Using elemental fluorine evolved in the cell, low-temperature fluorination of sulphur dioxide has been successfully carried out. | |
