Iodoform, production

In a 1-litre three-necked flask, fitted with a mechanical stirrer, reflux condenser and a thermometer, place 200 g. of iodoform and half of a sodium arsenite solution, prepared from 54-5 g. of A.R. arsenious oxide, 107 g. of A.R. sodium hydroxide and 520 ml. of water. Start the stirrer and heat the flask until the thermometer reads 60-65° maintain the mixture at this temperature during the whole reaction (1). Run in the remainder of the sodium arsenite solution during the course of 15 minutes, and keep the reaction mixture at 60-65° for 1 hour in order to complete the reaction. AUow to cool to about 40-45° (2) and filter with suction from the small amount of solid impurities. Separate the lower layer from the filtrate, dry it with anhydrous calcium chloride, and distil the crude methylene iodide (131 g. this crude product is satisfactory for most purposes) under diminished pressure. Practically all passes over as a light straw-coloured (sometimes brown) liquid at 80°/25 mm. it melts at 6°. Some of the colour may be removed by shaking with silver powder. The small dark residue in the flask solidifies on cooling. 

Iodoform (111,45, scale use 50 ml. conical flask recrystallise product in 25 ml. flask with short water condenser). 

In current industrial practice gas chromatographic analysis (glc) is used for quahty control. The impurities, mainly a small amount of water (by Kad-Fischer) and some organic trace constituents (by glc), are deterrnined quantitatively, and the balance to 100% is taken as the acetone content. Compliance to specified ranges of individual impurities can also be assured by this analysis. The gas chromatographic method is accurately correlated to any other tests specified for the assay of acetone in the product. Contract specification tests are performed on product to be shipped. Typical wet methods for the deterrnination of acetone are acidimetry (49), titration of the Hberated hydrochloric acid after treating the acetone with hydroxylamine hydrochloride and iodimetry (50), titrating the excess of iodine after treating the acetone with iodine and base (iodoform reaction). 

Condensation of vinyl chloride with formaldehyde and HCl (Prins reaction) yields 3,3-dichloro-l-propanol [83682-72-8] and 2,3-dichloro-l-propanol [616-23-9]. The 1,1-addition of chloroform [67-66-3] as well as the addition of other polyhalogen compounds to vinyl chloride are cataly2ed by transition-metal complexes (58). In the presence of iron pentacarbonyl [13463-40-6] both bromoform [75-25-2] CHBr, and iodoform [75-47-8] CHl, add to vinyl chloride (59,60). Other useful products of vinyl chloride addition reactions include 2,2-di luoro-4-chloro-l,3-dioxolane [162970-83-4] (61), 2-chloro-l-propanol [78-89-7] (62), 2-chloropropionaldehyde [683-50-1] (63), 4-nitrophenyl-p,p-dichloroethyl ketone [31689-13-1] (64), and p,p-dichloroethyl phenyl sulfone [3123-10-2] (65). 

The nitrous acid here acts on the alcohol in the same way as do the halogens in the production of chloroform and iodoform. 

The checkers also carried out the reaction using equimolar quantities of 2,3-dimethyl-2-butene and iodoform (0.1 mole each) and obtained 12.6-13.0 g. (56-58%) of the product. The submitters made the same observation. They found that the yield increased slightly as the mole ratio of olefin to iodoform was increased from 1 1 to 3 1. Use of a larger excess of olefin resulted in no further increase in yield. 

Formaldehyde-Starch Mixture is, accdg to Hackh s (1944), P 53 L, an antiseptic powder amyloform, used like iodoform. He calls (p 381-R) the product of reaction of formaldehyde starch glutol, while the name of glutol or gluloform is given in CondChemDict (1961), p 540-L to product obtd by the action of formaldehyde gelatin. This product exists as a clear transparent mass which may be pulverized or a white to yel powder. It is insol in oold w but sol in hot w, under pressure... 

Phenylhydrazone formation indicates a carbonyl compound. Since the negative Tollens test rules out an aldehyde, (A) must be a ketone. A negative iodoform test rules out the CH,C=0 group, and the reduction product, pentane, establishes the C s to be in a continuous chain. The compound is CHjCHjCOCHjCH,. 

The use of iodoform as the reagent precursor under Furukawa s conditions gives rise to a more complex scenario, since the additional C—I bonds can further react with an ethylzinc species (equation 8)" . The reaction of the iodo-substituted zinc carbenoid with an alkene will generate an iodo-substituted cyclopropane, whereas that involving the gem-dizinc carbenoid will lead to a cyclopropylzinc product. The evidence for the formation of a. gem-dizinc carbenoid was obtained not only by the analysis of the cyclopropanation products but also by the formation of rfi-iodomethane upon quenching the reagent with D2O/DCI. 

This reaction works equally well with chlorine or iodine and is known as the chloroform or iodoform reactions in these cases after the names of the products. 

Three common methods of production are described in the literature the action of iodine,1 sodium ethylate,2 or hydriodic acid 3 on iodoform. The last of these three methods has been worked out in more detail and is the one generally recommended for the preparation of methylene iodide in the laboratory. In addition, methylene iodide has been produced by the action of iodine on diazomethane 4 and by electrolysis of iodoacetic acid.5 It may also be made by the action of potassium iodide upon methylene chloride.Sa... 

This sequence is called the haloform reaction because it results in the production of chloroform, bromoform, or iodoform, depending upon the halogen used. The haloform reaction is a useful method for identification of methyl ketones, particularly when iodine is used, because iodoform is a highly insoluble, bright-yellow solid. The reaction also is very effective for the synthesis of carboxylic... 

The condensation is carried out in the usual manner in chloroform solution. The product separates from alcohol with 1 5 molecules of solvent of crystallisation, which can be removed at 110° C. It gives the iodoform test with iodine in aqueous sodium hydroxide. At 260° to 265° C. it decomposes. It is insoluble in w ater, but dissolves in hot alcohol or aqueous sodium hydroxide. Alcoholic ferric chloride gives a faint olive-green tint concentrated sulphuric acid gives no coloration in the cold, but on warming an olive-green tint appears, changing to deep red. The chloride may be converted to the oodde in the usual manner. 

When a base is used with a methy] ketone, the alpha carbon will become completely halogenated. This trihalo product reacts further with the base to produce a carboxylic acid and a haloform (chloroform, CHCI j bromoform, CHBr, or iodoform, CHIj). This is called the Haloform Reaction. 

Aloe latex is prepared by cutting transversely the leaf near the base and kept in an inclined position so that the latex contained in the specialized pericyclic cells, and sometimes in the adjacent parenchyma, flows out in about 6 h. No pressure must be applied or the product will be contaminated with the mucilage present in the inner part of the leaves. The latex obtained is bitter and yellow condensed to dryness, it becomes a shiny mass, similar to broken glass, of a yellowish green to red-black color. Slow evaporation, carried out at an inappropriate temperature, yields an opaque mass with a waxlike fracture. The taste is nauseating and bitter, and the odor sour, recalling that of rhubarb, apple-tart, or iodoform (Sollmann, 1944). 

This reaction has been used in qualitative analysis to indicate the presence of a methyl ketone. The product iodoform is yellow and has a characteristic odour. The reaction has some synthetic utility in the oxidative demethylation of methyl ketones if the other substituent on the carbonyl groups bears no enolizable a-protons. 

OHj OHaOH + 3NaI + 8H,0 = Na 003 + OHIs + NaOH + 5H2. The cathode should be of lead, and encased in parchment to prevent cathode hydrogen from destroying the product.2 The temperature should be 60-70° C. and anode current density 1-2 amps, per dm.2 with a voltage of 2-2 5 volts. The iodoform is produced at the rate of 500 grams per kilowatt-hour (1 3 grams per amp.-hour) and the current efficiency is about 90 per cent. 

The electrolysis is best performed as follows A solution of 13-15 g. calcined soda and 10 g. potassium iodide in 100 cc. water and 20 cc. alcohol is placed in a porous earthenware cylinder with platinum anode. The cathode, of nickel, is surrounded by a strong solution of sodium hydroxide. The electrolysis is carried out at a temperature of 70° C., with a current density at the anode of 1 amp. per 100 sq. cm., and is continued for 2-3 hours. After several hours the iodoform crystallizes out, the current yield being from 60-70 per cent. The chief by-product remaining in the mother liquor is sodium iodate. 

Iodoform2 from Acetone.—Teeple3 mentions a method by which almost the theoretical yield of iodoform can be obtained by the electrolysis of a potassium-iodide solution in the presence of acetone. No diaphragm is required, the essential feature being the gradual addition of a substance like hydrochloric acid, hydriodic acid, or, better, iodine, to neutralize the excess of potassium hydroxide as fast as it is formed. The tempera-, ture is kept below 25°, and the electrolyte thoroughly stirred in fact the same current conditions should be observed as in the case of chloroform above mentioned, the aim in this case also being to maintain the conditions always favorable for the production of a maximum amount of hypoiodite. 

When the halogen is iodine, the haloform product (iodoform) is a solid that separates out as a yellow precipitate. This iodoform test identifies methyl ketones, which halo-genate three times, then lose CI3 to give iodoform. 

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