Potassium metabisulphite

Pulp from ripe Golden apple was pressed in a mortar and filtered, thus obtaining a cloudy and dense juice. Potassium metabisulphite was added as antioxidant at a final concentration of 0.15 mg/mL. The pH of the prepared apple juices was 4.1 4.3. Depectinisation experiments were carried out loading the juice in the packed bed reactor and recycling for 30 min at 25 "C. The reaction mixture was then collected and the percentage reduction of viscosity measured as above described. The y-alumina spheres were abundantly washed with distilled water before performing the successive batch reaction. 

The sulphites, both normal and acid, are easily oxidised, and in solution readily undergo atmospheric oxidation with the formation of sulphates. The oxidation proceeds more readily in neutral than in acid solution,2 and is accelerated by warming. The change in SOa-content of a solution of potassium metabisulphite (0-1 per cent.) kept in a stoppered bottle, observed by titration at intervals of aliquot portions with standard iodine solution, has been observed to be as follows 3... 

Reduction by zinc dust yields an oil iodine in chloroform has no action, but chlorine in the same solvent gives selenium tetrachloride and chloroacetylacetone, and bromine yields lachrymatory products and a colourless crystalline substance of melting-point 180° C. Aqueous hydrogen sulphide causes slow decomposition, with liberation of sulphur and selenium. Potassium metabisulphite and sodium hydrogen sulphite transform selenium acetylacetone quantitatively into alkali selenodithionates, a reaction which affords the best known means of preparing these salts. 

Dichlorotelluridiacetic acid, 2 grams, is reduced by a solution of 2 8 grams of potassium metabisulphite in 25 c.c. of water, sulphur dioxide being evolved and a pale yellow solution containing grey needles resulting. This latter product is extracted repeatedly with small quantities of ether, tellurodiacetic acid being isolated in quantitative yield on removal of the solvent. Recrystallisation from acetone-... 

Elemental tellurium and methylene iodide yield di-iodomethyl tellurium di-iodide, M.pt. 131 C., which may be reduced by potassium metabisulphite to di-iodomethyl telluride, a yellow crystalline substance which changes to an orange polymeride at temperatures above 75° C. 

The types of compound obtainable by the condensation of tellurium tetrachloride and mixed ethers may be exemplified by the case of phenetole. The primary product obtained in the reaction is p-phenetyl telluritriehloride (I), which on heating with more phenetole gives Ws-p-phenetyl telluridichloride (II). The latter also occurs if an excess of phenetole be used in the initial condensation. Reduction of the trichloride by aqueous potassium metabisulphite at 0° C. produces bis-p-phenetyl ditelluride (III). 

The mother-liquor from the monoiodide gives p-anisyl methyltelluridi-iodide, CH3O.C6H4.Te(CH3)I2, a red crystalline substance, M.pt. 109° C., soluble in organic solvents. Reduction of this substance by aqueous potassium metabisulphite in the presence of ether yields p-anisyl methyl... 

Reduction of the telluritrichloride by aqueous potassium metabisulphite gives p -diphenoxydiphenyl ditelluride,... 

Tellurium 3-ethylpropionylacetone (2-Methyl-4-ethylcyclo-ielluropenianedione), formed by reducing the dichloride (1 mol.) with aqueous potassium metabisulphite (2 mols.), crystallises from alcohol as pale yellow needles, M.pt. 109° C., sparingly soluble in water. 

Reduction of the dichloride (8 7 grams) by 12 2 grams of potassium metabisulphite in 70 c.c. of cold water gives a quantitative yield of cyclotelluro-4 4-dimethylpentane-3 5-dione as transparent lemon-yellow refractive prisms from benzene, golden-yellow needles from alcohol or serrated needles from water, melting at 124° to 125° C. and subliming in a vacuum at 105° C. The dione is moderately soluble in cold chloroform, alcohol, or other organic solvents when warm, and moderately soluble in cold water. 

This is prepared by the general method of reduction of the dichloride using aqueous potassium metabisulphite. It crystallises from hot water or benzene-petroleum as yellow needles, melting without decomposition at 110° to 112° C., very soluble in cold acetone or hot benzene. It possesses residual acidity, dissolving in cold 5N sodium hydroxide to give an intensely yellow solution which blackens rapidly and then has an odour of methyl n-propyl ketone. 

Tellurium 3 - methylpropionylacetone (2 4-Dimethylcyclo-telluropentanedione) occurs when the preceding compound is reduced with potassium metabisulphite. The product readily dissolves in organic solvents or hot water, whilst in cold water it is more soluble than its alkylated homologues it is devoid of residual acidity, its aqueous solution being neutral to litmus. It crystallises from water or methyl alcohol as long, soft, pale golden needles or elongated prisms, M.pt. 125° to 126° C. with decomposition, and sublimes in a vacuum at 100° C. as short needles or prisms. 

Potassium pyrosulphite, K2S205.—On treatment of a hot saturated solution of potassium carbonate with sulphur dioxide, the pyrosulphite separates in monoclinic crystals, which are more stable than those of the primary sulphite. Its heat of formation from the elements is 369-4 Cal.8 It is employed in the preparation of photographic developers under the name potassium metabisulphite. ... 

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