Bisulfite compounds

The analyses can be carried out in the presence of /V-methy1o1 groups. On fabric, the formaldehyde bisulfite compound is decomposed by excess sodium carbonate and the Hberated sulfite is titrated with 0.1- or 0.01-N iodine solution (76). Commercial fabrics are seldom washed and dried before being used, and the free formaldehyde content may be between 50 and several hundred ppm, depending on finishing and storage conditions. 

A solution of 100 g of sodium bisulfite in 200 ml of water is added, and the stirring is continued for 10 hours with exclusion of air. A thick precipitate separates after a few minutes. The bisulfite compound is collected by suction filtration, washed with ether until colorless, and then decomposed in a flask with a lukewarm solution of 125 g of sodium carbonate in 150 ml of water. The ketone layer is separated, and the aqueous layer is extracted four times with 30-ml portions of ether. The combined organic layers are dried over anhydrous magnesium sulfate, the ether is removed at atmospheric pressure, and the residual oil is fractionated under reduced pressure through a short column. The cycloheptanone, bp 64-65°/ 2 mm, is obtained in about 40% yield. 

Benzyl alcohol, 23, 14 BeNZYLAMINE, a-METHYL-, 23, 68 Benzyl carbamate, 23, 14 Benzyl chloride, 21, 99 Benzyl chloroeormate, 23, 13 Benzyl cyanide, 23, 71 Bisulfite compound, use for purification of an aldehyde, 23, 78 use for purification of a ketone, 23, 79 Blood, defibrinated, 21, 53 Booster pump, use of, for hydrogenation, 23, 69... 

The pseudoionone bisulfite addition product, unlike that of citral, apparently decomposes rather slowly if the separation is made too soon, some undecomposed bisulfite compound is left in solution. This is later decomposed and, in contact with the alkali, polymerizes to a dark red gum. 

A considerably lower yield is obtained (50 per cent or less) if technical salicylaldehyde (not purified through the bisulfite compound) be employed. 

At any rate, the bisulfite compound of acetaldehyde has been shown to be present in wine. 

Ketoses do not form bisulfite addition compounds. This fact shows also that formation of the bisulfite compound of the sugar is not essential, since S02 prevents browning by ketoses also. 

Compounds of this type are much more stable than bisulfite compounds and therefore have low browning potential. 

Phenylglyoxal has been prepared from isonitrosoacetophenone through the bisulfite compound 2,3 or by treatment with nitro-sylsulfuric acid 4 or with nitrous acid.3 It also has been prepared by the oxidation of benzoylcarbinol with copper acetate,6 by heating bromophenacyl acetate,7 and by the oxidation of acetophenone with selenium dioxide.1... 

Chromium trioxide, 21, 6 24, 39, 76 Cinnamic acid, 20, 77 22, 26 24, 21 Cinnamoyl chloride, 20, 77 24, 21 Citral, bisulfite compound, 23, 78 purification of, 23, 78 Claisen condensation, with acetone and ethyl formate, 27, 92 with ethyl oxalate and ethyl succinate, 26,42... 

The products are useful for two reasons. They are usually crystalline and so can be used to purify liquid aldehydes by recrystallization. This is of value only because this reaction, like several you have met in this chapter, is reversible. The bisulfite compounds are made by mixing the aldehyde or ketone with saturated aqueous sodium bisulfite in an ice bath, shaking, and crystallizing. After purification the bisulfite addition compound can be hydrolysed back to the aldehyde in dilute aqueous acid or base. 

The reversibility of the reaction makes bisulfite compounds useful intermediates in the synthesis of oilier adducts from aldehydes and ketones. For example, one practical method for making cyanohydrins involves bisulfite compounds. The famous practical book Vogel3 suggests reacting acetone first with sodium bisulfite and then with sodium cyanide to give a good yield (70%) of the cyanohydrin. 

What is happening here The bisulfite compound forms first, but only as an intermediate on the route to the cyanohydrin. When the cyanide is added, reversing the formation of the bisulfite compound provides the single proton necessary to to give back the hydroxyl group at the end of the reaction. No dangerous HCN is released (always a hazard when cyanide ions and acid are present together). 

The bisulfite compound of formaldehyde (CH2O) has special significance. Earlier in this chapter we mentioned the difficulty of working with formaldehyde because it is either an aqueous solution or a dry polymer. One readily available monomeric form is the bisulfite compound. It can be made in water (in which it is soluble) but addition of ethanol (in which it isn t) causes it to crystallize out. 

The second reason that bisulfite compounds are useful is that they are soluble in water. Some small (that is, low molecular weight) aldehydes and ketones are water-soluble—acetone is an example. But most larger (more than four or so carbon atoms) aldehydes and ketones are not. This does not usually matter to most chemists as we often want to carry out reactions in organic solvents rather than water. But it can matter to medicinal chemists, who make compounds that need to be compatible with biological systems. And in one case, the solubility of bisulfite adduct in water is literally vital. 

The solution is to make a bisulfite compound from it. You may ask how this is possible since dapsone has no aldehyde or ketone—just two amino groups and a sulfone. The trick is to use the formaldehyde bisulfite compound and exchange the OH group for one of the amino groups in dapsone. 

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