Alkyl picrates

Nitro substitution increases the leaving-group ability of ArO groups, and alkyl picrates [2,4,6-R0C6H2(N02)3] react at rates comparable to tosylates Sinnott, M.L. Whiting,... 

Gazzolo (1900) thought that the intense colours produced from alkyl picrates and alkoxides could be best described by the quinonoid structure 1 (R = R = alkyl). The first strong chemical evidence that this was indeed the case was provided by Meisenheimer (1902). He obtained identical compounds by the addition of potassium methoxide to 2,4,6-trinitrophenetole and potassium ethoxide to 2,4,6-trinitroanisole. Acidification produced in each case a mixture of methyl and ethyl picrates. This led Meisenheimer to the conclusion that these compounds... 

Spectroscopic Data for 1 1 Adducts from Alkyl Picrates... 

Boiling poinl, C S Alkyl 1 Naph Alkyl Picrate of 2 4 Di nitrO 2 4 Di ... 

Melting Boiling S-Alkyl I-Naph- Alkyl Picrate of 2,4-Dimtro 2,4-Dinitro- ... 

The infrared spectra of adducts such as (5) formed between alkyl picrates and alkoxides show changes relative to the parent compounds that are consistent with a fully covalent structure. A series of strong bands between 1225 and 1040cm" is typical of ketals [118, 119]. Many sigma adducts are intensely colored, and attempts have been made to correlate UV-visible spectra with structural features [120]. However, these spectra do not generally provide such precise information as do NMR studies. Nevertheless, the absorption intensity usually obeys the Beer-Lambert law, so that absorption is directly proportional to concentration, and this is very useful in the determination of concentrations in kinetic and equilibrium studies. 

S-Alkyl-iso-thiuronium picrates. Alkyl bromides or iodides react with thiourea in alcoholic solution to produce S-alkyl-iso-thiuronium salts, which yield picrates of sharp melting point ... 

Place a mixture of 0-5 g. of finely powdered thiourea, 0-5 g. of the alkyl halide and 5 ml. of alcohol in a test-tube or small flask equipped with a reflux condenser. Reflux the mixture for a j)eriod depending upon the nature of the halide primary alkyl bromides and iodides, 10-20 minutes (according to the molecular weight) secondary alkyl bromides or iodides, 2-3 hours alkyl chlorides, 3-5 hours polymethy lene dibromides or di-iodides, 20-50 minutes. Then add 0 5 g. of picric acid, boil until a clear solution is obtained, and cool. If no precipitate is obtained, add a few drops of water. RecrystaUise the resulting S-alkyl-iso-thiuronium picrate from alcohol. 

Picrates of p-naphthyl alkyl ethers. Alkyl halides react with the sodium or potassium derivative of p-naphthol in alcoholic solution to yield the corresponding alkyl p-naphthyl ethers (which are usually low m.p. solids) and the latter are converted by alcoholic picric acid into the crystalline picrates ... 

Mix together 1 0 g. of pure p-naphthol and the theoretical quantity of 50 per cent, potassium hydroxide solution, add 0-5 g. of the halide, followed by sufficient rectified spirit to produce a clear solution. For alkyl chlorides, the addition of a little potassium iodide is recommended. Heat the mixture under reflux for 15 minutes, and dissolve any potassium halide by the addition of a few drops of water. The p-naphthyl ether usually crystallises out on cooling if it does not, dilute the solution with 10 per cent, sodium hydroxide solution untU precipitation occurs. Dissolve the p-naphthyl ether in the minimum volume of hot alcohol and add the calculated quantity of picric acid dissolved in hot alcohol. The picrate separates out on cooling. Recrystallise it from rectified spirit. 

HaUde B.P. M.P.. 20 20 D 1 i. 4nUlde i i a-Naphtha- llde Alkyl 1 Mercuric i Halide S-Alkyl-ito- thiuronlum Picrate Picrate of Q-naphthyl ether... 

Alkylselenazoles are oily alkaline liquids possessing a smell similar to that of the corresponding thiazole or pyridine derivatives. The crystalline picrates or 3-methylselenazolium iodides have been used for the purpose of characterization. Alkyl derivatives are partially soluble in water aryl derivatives are insoluble. 

Lukes studied the reaction of N-methyl lactams with Grignard reagents. With the five- (39-42) and six-membered (43-47) rings, 2,2-dialkylated bases (16, = 1,2) are formed as by-products in addition to the l-methyl-2-alkyl pyrrolines (15, = 1) or l-methyl-2-alkyl piperideines (15, =2). Aromatic Grignard reagents afford only the unsaturated bases, probably because of steric factors (48,49). Separation of enamines and 2,2-dialkylated amines from each other can be easily achieved since the perchlorates of the enamines and the picrates of 2,2-dialkylated bases crystallize readily. Therefore enamines can be isolated as crystalline perchlorates and the 2,2-dialkylated bases as crystalline picrates. Some authors who repeated the reactions isolated only pyrrolines (50,57) or, by contrast, 2,2-dialkylated bases (52). This can be explained by use of unsuitable isolation techniques by the authors. 

Favretto and Tunis [198] extracted polyoxyethylene alkyl phenyl ethers as picrates into an organic solvent, complexed the polymer with sodium ion, and measured the absorption complex. This is one of the few specific methods available. 

Hexamethyleneimine and its benzo derivatives are typical secondary amines and undergo electrophilic substitution at nitrogen, e.g. alkylation and acylation, under standard conditions. Most form stable hydrochlorides and simple derivatives such as picrates (B-67MI51600). Table 4 contains pjRTa values of some azepines. 

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