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Heading 2925 : Carboxyimide-function compounds (including saccharin and its salts) and imine-function compounds.
(A) IMIDES
Imideshave the general formula (R=NH), where R is a dibasic acyl radical. (1) Saccharin or 1,2-benzisothiazolin-3-one 1,1-dioxide and its salts. Saccharin is an odourless, white crystalline powder having a very sweet taste; its sodium and ammonium salts have a lower sweetening power but are more soluble. Tablets consisting solely of one of these products remain in this heading.
Preparations, used in human diets, consisting of a mixture of saccharin or its salts and a foodstuff, such as lactose, are however excluded from this heading and fall in heading 21.06 (see Note 1 (b) to Chapter 38). Those preparations consisting of saccharin or its salts and substances, other than a foodstuff, such as sodium hydrogencarbonate (sodium bicarbonate) and tartaric acid fall in heading 38.24. (2) Succinimide, used in chemical synthesis. (3) Phthalimide, used in chemical synthesis. (4) Glutethimide. A psychotropic substance - see the list at the end of Chapter 29.
Organic imide derivatives of inorganic acids are classified in heading 29.29. (B) IMINES
Imines, like imides, are characterised by the group =NH, but it is linked to a non-acidic organic radical : (R2C=NH). (1) Guanidines. The action of cyanamide on ammonia gives an imino-urea known as guanidine; this can be regarded as derived from urea by replacing the oxygen of the (C=O) group by an imino group (=NH):
H2NCONH2 (urea) .......................................... (H2N)2C=NH (guanidine)
Guanidine is also formed in the oxidation of proteins; it can also be obtained synthetically. It is crystalline, colourless and deliquescent.
Its derivatives include : (a) Diphenylguanidine. Rubber accelerator. (b) Di-o-tolylguanidine. Rubber accelerator. (c) o-Tolyldiguanide. Rubber accelerator. (2) Aldimines. These have the general formula (RCH=NR1) where R and R1 are alkyl or aryl radicals (methyl, ethyl, phenyl, etc.) or sometimes hydrogen.
They constitute the products known as Schiff's bases, the most important of which are : (a) Ethylideneaniline. (b) Butylideneaniline. (c) Aldol-a- and -b-naphthylamines. (d) Ethylidene-p-toluidine.
All these products are used in the rubber industry. (3) Imino ethers. (4) Amidines. (5) 2,6-Dichlorophenolindophenol. This heading excludes, however, cyclic polymers of aldimines (heading 29.33).
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