Tri-iodomethane

This reaction is often called the iodoform reaction. Iodoform was an old name for tri-iodomethane, just as chloroform is still used for trichloromethane. It is one of the rare cases where nucleophilic substitution at a carbonyl group results in the cleavage of a C-C single bond. 

With alkenes, di-iodomethane (5.67) or tri-iodomethane (5.68) reacts photochemically to form cyclopropanes. The intermediate is... 

Iodoform, CHI3, tri-iodomethane, is formed when alcohol and certain other compounds (66) are treated with iodine in the presence of an alkali. It can be prepared by adding iodine to a warm aqueous solution of alcohol or acetone which contains sodium carbonate. The iodoform, which separates as a yellow precipitate, is purified by crystallization from dilute alcohol. It crystallizes in yellow, lustrous, six-sided plates, which melt at 119 , and have a peculiar, very characteristic odor. The reactions by which alcohol is converted into iodoform are analogous to those as the result of which chloroform is obtained from alcohol. The formation of iodoform is often used as a test for ethyl alcohol, but as other substances, such as acetone, isopropyl alcohol, and aldehyde yield iodoform when warmed in alkaline solution with iodine, the test is not reliable unless it is known that the other substances which respond to it are absent. Most of the compounds which yield iodoform when treated in this way contain the group CH3.C linked to oxygen. 

The reaction of methyl ketones with sodium iodate(l) gives iodoform (tri-iodomethane), which is a yellow soUd with a characteristic smeU. This reaction is used in the Iodoform test to identify methyl ketones. It also gives a positive result with a secondary alcohol of the formula RCH(OH)CH3 (which is first oxidized to a methylketone) or... 

Iodoform (tri-iodomethane, CAS no. 75-47-8). This releases iodine under the influence of light and (especially) temperature. It is mostly available as a bismuth-iodoform paste. The patch-test concentration is 5% pet. Allergic reactions do occur. 

When separated from the reaction mixture, the yellow crystals of tri-iodomethane can be positively identified by their melting point of 119°C. 

The tri-iodomethane test can also be used to identify the presence of a secondary alcohol group on the carbon atom adjacent to a methyl group. This CH3CH(OH)—group is firstly oxidised by the alkaline iodine solution. This oxidation forms a methyl ketone, RCOCH, which then reacts via the two steps shown above to give the yellow tri-iodomethane precipitate, CHI3. 

You should note that there are two organic products formed in this reaction one is tri-iodomethane and the other is the sodium salt of a carboxylic acid. 

A yellow precipitate of tri-iodomethane is formed in a positive test. 

Dibenz[r,e,]azcpinium salts, e.g. 3 and 6, arc also obtained by O- and 5-alkylation of 6,7-dihydro-5//-dibenz[f,e]azepin-7-ones 2 and -7-thiones 5 with trimethyloxonium tetrafluo-roborate.181 iodomethane,181 or methyl trifluoromethanesulfonate.12 Treatment of the tri-fluoromethanesulfonates 3 and 6 (X = OTf), or the tetrafluoroborate 6 (X = BF4) with 2 M sodium hydroxide in dichloromethane liberates the free bases 4 and 7, respectively.7,181... 

Reaction of the quaternized salts of 4-ethoxycarbonyl-3,5-dimethyl-f-phenylpyttolo(furo or thieno)[2,3-c]pyrazole 34 with the iodomethane quaternary salts of pyridine, quinoline, and isoquinoline in ethanol with catalytic piperidine gave 3-[4(f)]-monomethine cyanine dyes (e.g., 35). Additionally, 3-[2(4)]-trimethine cyanine dyes and 4-[2(4)]-di-3[2(4)]-tri-mixed methine cyanine dyes (e.g., 36 and 37, respectively) were similarly prepared from the intermediates derived by reaction of 34 with triethyl orthoformate in the presence of piperidine (Scheme 8) <2002CCS106f>. 

An unknown reducing disaccharide is found to be unaffected by invertase enzymes. Treatment with an a-galactosidase cleaves the disaccharide to give one molecule of D-fructose and one molecule of D-galactose. When the disaccharide is treated with excess iodomethane and silver oxide and then hydrolyzed in dilute acid, the products are 2,3,4,6-tetra-(9-methyl-galactose and 1,3,4-tri-O-methylfructose. Propose a structure for this disaccharide, and give its complete systematic name. 

An example of reaction type (c) in Table 5-4 is the well-known Menschutkin reaction [30] between tertiary amines and primary haloalkanes yielding quaternary ammonium salts. Its solvent dependence was studied very thoroughly by a number of investigators [51-65, 491-496, 786-789]. For instance, the reaction of tri-n-propylamine with iodomethane at 20 °C is 120 times faster in diethyl ether, 13000 times faster in chloroform, and 110000 times faster in nitromethane than in -hexane [60]. It has been estimated that the activated complex of this Menschutkin reaction should have a dipole moment of ca. 29 10 Cm (8.7 D) [23, 64], which is much larger than the dipole moments of the reactant molecules (tris- -propylamine 2.3 10 Cm = 0.70 D iodomethane 5.5 10-3 1 64 D) [64]. 

Sn2 reaction of tris(n-propyl)amine with iodomethane at 20 °C [49, 50]. 

In addition to the application of SnI reactions as model reactions for the evaluation of solvent polarity, Drougard and Decroocq [48] suggested that the value of Ig kj for the Sn2 Menschutkin reaction of tri-n-propylamine and iodomethane at 20 °C -termed according to Eq. (7-21) - should also be used as a general measure of solvent polarity. 

Ig k2 for the Menschutkin reaction of tri- -propylamine with iodomethane (Drougard and Decroocq) standard molar entropy change standard molar entropy of activation solvophobic power of a solvent (Abraham)... 

When enantiopure (+)-(/ )-5-methyl-2-cyclohexenone is treated with lithium phenylthio(tri-methylstannyl)cuprate followed by iodomethane in hexamethylphosphoric triamide, a single product is obtained with [a]n8 +134 (CH,OH)16. 

Reaction of xanthine with triethylsilylamine gives 0, 0 ,A -tris(triethylsilyl)xanthine which can be methylated with iodomethane at room temperature to give bis-silylated 7-methyl-xanthine (33). At 60 "C, alkylation leads to the 0 -monosilylated 3,7-dimethyl derivative 34. Hydrolysis yields 7-methylxanthine or theobromine. 

Huang-Minlon reduction of a similar compound, the method was inapplicable. So, we adopted the method of radical reduction of xanthate (+)-65 instead.42 Ketone (+)-63 was stereoselectively reduced with lithium tri-sec-butylborohydride (L-Selectride), yielding axial alcohol (+)-64 in 92% yield, which was then con-verted to xanthate (+)-65 in quantitative yield by treatment of lithium alkoxide of the alcohol with carbon disulfide and then with iodomethane. Xanthate (+)-65 was next reduced with tributyltin hydride, giving the desired methylene compound (+)-66 in 92% yield. After deprotection of the acetal group of (+)-66 (98% yield), ketone (+)-67 was converted to olefin (-)-68 in 98% yield by formation of tosyl-... 

Similar addition reactions were observed with the bridged [l.l.l]propellane system tetra-cyclo[5.1.0.0 .0 ]octane (16) when reacted with diethyl ether, carbon tetrachloride, bromo-chloromethane, iodomethane, tert-butyl bromide, benzyl bromide and tri(butyl)tin hydride. ... 

The trithiodcltatc dianion 34 was trimethylated by iodomethane to provide the 1,2,3-tris(methylsulfanyl)cyclopropenylium salts 35 and 36. ... 

It was shown by us that the reaction of P with CF3I is not limited to the condensed or liquid phase. Red phosphorus is also alkylated by trifluoro-iodomethane vapor over a copper catalyst The products are the same as in the liquid reaction but in reduced yield and different composition. The mono-and dialkylated compounds are the major products wliich is the reverse of the liquid system where the tris (trifluoromethyl)phosphine is usually the dominant product. This indicates that the phosphorus dihalide is a primary product of the reaction and not a decomposition or disproportionation product. 

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