Sulphur melting-points

The student should read Sections 1,10 to 1,16 carefully before commencing any experimental work. A supply of melting point capillaries is prepared as described in Section 11,10 (compare Fig. 77, R , I). The apparatus illustrated in Fig. 77. 10, 2, a is assembled with concentrated sulphuric acid as the bath liquid the thermometer selected should have a small bulb. The melting points of pure samples of the following compounds are determined in the manner detailed in Section 11,10 —... 

Drop 1 g. of sodium into 10 ml. of ethyl alcohol in a small flask provided with a small water condenser heat the mixture until all the sodium has dissolved. Cool, and add 1 g. of the ester and 0-5 ml. of water. Frequently the sodium salt of the acid will be deposited either at once or after boiling for a few minutes. If this occurs, filter oflF the solid at once, wash it with a little absolute ethyl alcohol (or absolute methylated spirit), and convert it into the p-bromophenacyl ester, p-nitro-benzyl ester or S-benzyl-tso-thiuronium salt (for experimental details, see Section 111,85). If no solid separates, continue the boiling for 30-60 minutes, boil oflF the alcohol, allow to cool, render the product just neutral to phenolphthalein with dilute sulphuric or hydrochloric acid, convert the sodium salt present in solution into a crystalline derivative (Section 111,85), and determine its melting point. 

Now take another batch of sulphur flowers, but this time heat it well past its melting point. The liquid sulphur gets darker in colour and becomes more and more viscous. Just before the liquid becomes completely unpourable it is decanted into a dish of cold water, quenching it. When we test the properties of this quenched sulphur we find that we have produced a tough and rubbery substance. We have, in fact, produced an amorphous form of sulphur with radically altered properties. 

To prepare sabinenic acid for the identification of the terpene, Wallach operates as follows 10 grams of the crude terpene are mixed with the theoretical amount of potassium permanganate in water at ice temperature. The oxide of manganese is filtered off, the liquid rendered acid and extracted with ether, and the ethereal solution shaken with caustic soda solution. The sodium salt is very sparingly soluble, and is precipitated, collected, and decomposed with dilute sulphuric acid and purified by a further solution in ether. It must be well dried in a desiccator before its melting-point is determined. Sabinene has the following constitution —... 

When submitted to oxidation by a 2 per cent, solution of permanganate, pinononic acid, CgHj Og, melting at 128° to 129° C., the semi-carbazone of which melts at 204° C. Lastly the constitution of verbenone, as expressed by the above formula, is further confirmed by the fact that the bicyclic system is convertible into a monocyclic system by boiling with 25 per cent, sulphuric acid, with the formation of acetone and 3-methylcyclohexene-(2)-one-(l). This cyclohexenone has been characterised by its semi-carbazone (melting-point 198° C.) and by its conversion into y-acetobutyric acid (melting-point 36° C). The oily liquid, which did not react with sulphite, was submitted to benzoylation after dilution with pyridine. It thus gave rise to a benzoate from which was... 

Platinum is unaffected by most organic compounds, although some compounds may catalytically decompose or become oxidised on a platinum surface at elevated temperatures, resulting in an etched appearance of the metal. Carbon and sulphur do not attack platinum at any temperature up to its melting point. Molten platinum may dissolve carbon, but the solubility of the latter in solid solution is virtually zero. 

Reactions of contaminants in the fuel or air in the combustion zone can result in the formation of compounds which can condense as molten salts onto cooler components in the system. This type of process can occur when fuels containing sulphur or vanadium are burnt. In the case of sulphur contaminants, alkali sulphates form by reactions with sodium which may also be present in the fuel or in the combustion air, and for vanadium-containing fuels low-melting-point sodium vanadates or vanadium pentoxide are produced, particularly when burning residual oils high in vanadium. Attack by molten salts has many features in common which will be illustrated for the alkali-sulphate-induced attack, but which will be subsequently shown to be relevant to the case of vanadate attack. 

There are two basic crystallisation forms for sulphur - monoclinic and rhombic. Rhombic is the most stable form, at least up to 96 °C the other types revert to this stable form at a rate dependant upon temperature. When sulphur solidifies from the molten state (melting point 114 °C) the crystalline form which occurs is monoclinic (needle-like crystal structure). Below 96 °C, the monoclinic form becomes metastable and changes into the rhombic form. 

Preparation A mixture of phenol and formaldehyde is taken in the distillation vessel. To this hydrochloric acid or sulphuric acid or oxalic acid is added. Now the reaction mixture is heated under reflex at about 100-120°C for 2-4 hours. Water is a by-products which is distilled off at the atmospheric pressure. The resin to obtained is having the Melting point 65-75°C. 

The heating liquid is pure concentrated sulphuric acid, with which the bulb of the flask is three-quarters filled. The substance, in powder form, is introduced into a small, thin-walled capillary tube. Such tubes are made as follows from test tubes (preferably from damaged tubes which must, however, be clean and dry ). The tubes are rotated in the flame of the blow-pipe till soft and then drawn out rapidly already after short practice the student can strike the correct diameter, which should be 1 0-1 -5 mm. internally. Suitable portions of the drawn-out material are cut off with scissors. It is convenient to cut double lengths (about 12 cm.), so that by sealing each length in the middle (micro-burner) two melting-point tubes are obtained ready for use. 

Benzyl cyanide (40 g. = 0 33 mole) is heated in a round-bottomed flask (capacity 0-5 1.), with a mixture of 50 c.c. of concentrated sulphuric acid and 30 c.c. of water. The flask is provided with an upright air condenser, and is placed in a conical (Babo) air bath. The heating is continued until the appearance of small bubbles of vapour indicates that a reaction, which rapidly becomes violent, has set in the liquid boils up, and white fumes are emitted. It is allowed to cool and then two volumes of water are added. After some time the phenylacetic acid which has crystallised out is filtered off with suction. If a sample of the material does not form a clear solution with sodium carbonate in water (presence of phenylacetamide), the whole of the crude material is shaken with sodium carbonate solution and the mixture is filtered. From the clear filtrate phenylacetic acid is reprecipitated with sulphuric acid, and can be recrystallised directly from a rather large volume of hot water or, after drying, from petrol ether. Because of its low melting point (76°) it often separates at first as an oil, but it can also be conveniently purified by distillation in vacuo from a sausage flask.2... 

To a mixture of 14 c.c. (25 g.) of concentrated sulphuric acid and 10 c.c. (15 g.) of fuming nitric acid in an open flask 10 g. of nitrobenzene are gradually added (fume chamber). The mixture is then heated on the water bath for half an hour with frequent shaking. The reaction mixture is cooled somewhat and then poured with stirring into cold water. The dinitrobenzene solidifies, is filtered with suction, washed with water, pressed on porous plate, and crystallised from alcohol. Melting point 90°. Yield 10-12 g. 

The cooled melt is gradually mixed with 500 g. of crushed ice, the liquid thus obtained is filtered and 120 g. of nitric acid (d. 1-4) are added to the brown filtrate, which is then heated at 50° for half an hour. After the solution has stood for twelve hours at ordinary temperature, the greater part of the dinitronaphtholsulphonic acid produced will have separated. It is filtered off and crystallises from hot dilute hydrochloric acid in small yellow needles which are dried first on porous plate and then in a desiccator over sulphuric acid and potassium hydroxide. Melting point 151°. Yield about 85 per cent of theoretical. 

---