Pyridine solutions

Acyl halides, both aliphatic and aromatic, react with the sodium derivative, but the product depends largely on the solvent used. Thus acetyl chloride reacts with the sodium derivative (E) suspended in ether to give mainly the C-derivative (t) and in pyridine solution to give chiefly the O-derivative (2). These isomeric compounds can be readily distinguished, because the C-derivative (1) can still by enolisation act as a weak acid and is therefore... 

The reaction is readily illustrated by the formation of crystalline sorbic acid by the condensation of crotonaldehyde and malonic acid in hot pyridine solution ... 

For some phenols whose esters are readily hydrolysed, it is advantageous to add the powdered chloride to a pyridine solution of the phenol, warm the mixture on the water-bath for ca. 15 minutes, cool and pour into water, when the sulphonate will separate. 

The absolute concentration of a reagent e.g., the exact amount of acetic anhydride in the above pyridine. solution) need not be determined, since if the same amount of the reagent is used in the actual and in the control experiments, the difference gives at once the actual amount used. 

Ootonic acid may be prepared by condensing acetaldehyde with malonic acid in pyridine solution in the presence of a trace of piperidine (Doebner reaction see discussion following Section IV,123). 

Feebly basic amines, e.g., the nitroanilines, generally react so slowly with benzenesulphonyl chloride that most of the acid chloride is hydrolysed by the aqueous alkali before a reasonable yield of the sulphonamide is produced indeed, o-nitroaniline gives little or no sulphonamide under the conditions of the Hinsberg test. Excellent results are obtained by carrying out the reaction in pyridine solution ... 

Most amines react so rapidly in pyridine solution that the reaction is usually complete after refluxing for 10-15 minutes. 

Benzenesulphonyl chloride reacts with primary and secondary, but not with tertiary, amines to yield substituted sulphonamides (for full discussion, see Section IV,100,3). The substituted sulphonamide formed from a primary amine dissolves in the alkaline medium, whilst that produced from a secondary amine is insoluble in alkali tertiary amines do not react. Upon acidifying the solution produced with a primary amine, the substituted sulphonamide is precipitated. The reactions form the basis of the Hinsberg procedure for the separation of amines see Section IV,100,(viii) for details. Feebly basic amines, such as o-nitroaniline, react slowly in the presence of allcali in such cases it is best to carry out the reaction in pyridine solution see Section IV,100,3. ... 

Carbocyanines with three methine groups can be prepared using Pvo equivalents of selenazolium quaternary salt and one equivalent of ethyl orthoformate in pyridine solution (53). 

Iminoselenazolidin-4-one is benzoylated on the imino" nitrogen with benzoyl chloride in pyridine solution (77),... 

Aromatic thioamides can be prepared as described in the literature by different ways, either by S -> O exchange between the corresponding benzamides and phosphorus pentasulfide in pyridine solution in the presence of triethylamine (65, 646) as strong base, or by action of H2S on the appropriate nitrile with pyridine and triethylamine solvents using the method of Fairfull et al. (34, 374, 503). In this reaction, thioacetamide in acidic medium can also be used as a H2S generator with dimethylform-amide as the solvent (485). 

In a similar way, 6-amino-l,3-dimethyluraciles (63) undergo easy conversion to the corresponding thiazolopyrimidines (64) upon treatment with thionyl chloride in pyridine solution (except with R = CF3, where SO2CI2 is more effective in the absence of pyridine) (Scheme 29) (654), with R = H, CO2H, C02Et, Ph, or CF3. 

Acid-cataly2ed hydroxylation of naphthalene with 90% hydrogen peroxide gives either 1-naphthol or 2-naphthiol at a 98% yield, depending on the acidity of the system and the solvent used. In anhydrous hydrogen fluoride or 70% HF—30% pyridine solution at — 10 to + 20°C, 1-naphthol is the product formed in > 98% selectivity. In contrast, 2-naphthol is obtained in hydroxylation in super acid (HF—BF, HF—SbF, HF—TaF, FSO H—SbF ) solution at — 60 to — 78°C in > 98% selectivity (57). Of the three commercial methods of manufacture, the pressure hydrolysis of 1-naphthaleneamine with aqueous sulfuric acid at 180°C has been abandoned, at least in the United States. The caustic fusion of sodium 1-naphthalenesulfonate with 50 wt % aqueous sodium hydroxide at ca 290°C followed by the neutralization gives 1-naphthalenol in a ca 90% yield. 

Arsenic. Total arsenic concentration can be determined by reduction of all forms to arsine (AsH ) and collection of the arsine in a pyridine solution of silver diethyldithiocarbamate. Organoarsenides must be digested in acidic potassium persulfate prior to reduction. The complex that forms is deep red, and this color can be measured spectrophotometricaHy. Reduction is carried out in an acidic solution of KI—SnCl2, and AsH is generated by addition of 2inc. 

Specifications, Analysis, and Toxicity. Dicyandiamide is identified quaHtatively by paper chromatography and quantitatively by ultraviolet spectrometry of the chromatogram. More commonly, total nitrogen analysis is used as a purity control or the dicyandiamide is converted by hydrolysis to guanylurea, which is determined gravimetrically as the nickel salt (50). Methods based on the precipitation of silver dicyandiamide picrate are sometimes used (51). Dicyandiamide can also be titrated with tetrabutylammonium hydroxide ia pyridine solution. Table 4 gives a typical analysis of a commercial sample. Dicyandiamide is essentially nontoxic. It may, however, cause dermatitis. 

The other analytical methods necessary to control the typical specification given in Table 5 are, for the most part, common quality-control procedures. When a chemical analysis for purity is desired, acetylation or phthalation procedures are commonly employed. In these cases, the alcohol reacts with a measured volume of either acetic or phthalic anhydride in pyridine solution. The loss in titratable acidity in the anhydride solution is a direct measure of the hydroxyl groups reacting in the sample. These procedures are generally free from interference by other functional groups, but both are affected adversely by the presence of excessive water, as this depletes the anhydride reagent strength to a level below that necessary to ensure complete reaction with the alcohol. Both procedures can be adapted to a semimicro- or even microscale deterrnination. 

Preferably, a few drops of the pyridine solution are rubbed first with a little water to provide seeding crystals so that the product will... 

The formation of a A -3-keto-19-norsteroid from the A -3-keto-19-acid in hot pyridine solution was first reported by Hagiwara." The same product is also obtained from the j ,y-unsaturated acid under identical con-... 

Of the four possible 5-deoxy-pent-4-enofuranoses, the D-erythro-isomer was of interest as a potential source of derivatives of L-lyxofuranose. For this purpose, a vinyl ether having the D-en/ hro-configuration has been prepared from derivatives of D-ribose. Condensation of D-ribose with acetone in the presence of methanol, cupric sulfate and sulfuric acid at 30°C., as described by Levene and Stiller(30) afforded a sirupy product consisting mainly of methyl 2,3-O-isopropylidene-D-ribofuranose (40). Treatment of a pyridine solution of the sirup with tosyl chloride... 

O-isopropylidene derivative (57) must exist in pyridine solution in a conformation which favors anhydro-ring formation rather than elimination. Considerable degradation occurred when the 5-iodo derivative (63) was treated with silver fluoride in pyridine (36). The products, which were isolated in small yield, were identified as thymine and l-[2-(5-methylfuryl)]-thymine (65). This same compound (65) was formed in high yield when the 5 -mesylate 64 was treated with potassium tert-hx Xy -ate in dimethyl sulfoxide (16). The formation of 65 from 63 or 64 clearly involves the rearrangement of an intermediate 2, 4 -diene. In a different approach to the problem of introducing terminal unsaturation into pento-furanoid nucleosides, Robins and co-workers (32,37) have employed mild base catalyzed E2 elimination reactions. Thus, treatment of the 5 -tosylate (59) with potassium tert-butylate in tert-butyl alcohol afforded a high yield of the 4 -ene (60) (37). This reaction may proceed via the 2,5 ... 

Alcohols react with p-toluenesulfonyl chloride (tosyJ chloride, p-TosCl) in pyridine solution to yield alkyl tosylates, ROTos (Section 11.1). Only the 0-H bond of the alcohol is broken in this reaction the C—O bond remains intact, so no change of configuration occurs if the oxygen is attached to a chirality center. The resultant alkyl tosylates behave much like alkyl halides, undergoing both SN1 and Sjsj2 substitution reactions. 

Esterification is normally carried out by treating the carbohydrate with an acid chloride or acid anhydride in the presence of a base (Sections 21.4 and 21.5). All the —OH groups react, including the anomeric one. For example, /3-o-glucopyranose is converted into its pentaacetate by treatment with acetic anhydride in pyridine solution. 

In the context of copper catalysis in important synthetic dediazoniations of arene-diazonium ions, Starkey s group (Bolth et al., 1943, Whaley and Starkey, 1946) isolated blue pyridine complexes with the constitution ArCu(C5H5N)3 by adding copper powder to pyridine solutions of ArNjBF4. However, it is unlikely that arylcopper is a relevant intermediate in these reactions (see Sec. 8.6). 

In aqueous pyridine solution, most diaryl sulphoxides may be oxidized to the corresponding sulphones with (dichloroiodo)benzene in reasonable yields103. The reaction involves nucleophilic attack by the sulphoxide on the electrophilic chlorine-containing species, yielding an intermediate chlorosulphonium ion which then reacts with water producing the sulphone. If the sulphoxide is optically active, then an optically active sulphone is produced in excellent optical yield when the reaction is carried out in oxygen-18 labelled water104, as indicated in equation (33). 

Within the wide range of phosphorus compounds described as activating agents for polyesterification reactions,2,310 triphenylphosphine dichloride and diphenylchlorophosphate (DPCP) were found to be the most effective and convenient ones. In pyridine solution, DPCP forms a A-phosphonium salt which reacts with the carboxylic acid giving the activated acyloxy A -phosphonium salt. A favorable effect of LiBr on reaction rate and molar masses has been reported and assumed to originate from the formation of a complex with the A-phosphonium salt. This decreases the electron density of the phosphorus atom... 

Thionyl chloride is another activating agent employed for reactions between aromatic carboxylic acids and phenols in pyridine solution. The mechanism suggested does not involve the formation of an acid chloride but assumes the existence of an intermediary mixed sulfinic anhydride which undergoes reaction with phenolic endgroups (Scheme 2.32).311... 

Primary, secondary, and tertiary alcohols can be converted to any of the four halides by treatment with the appropriate NaX, KX, or NH4X in polyhydrogen fluoride-pyridine solution." This method is even successful for neopentyl halides. Another reagent that converts neopentyl alcohol to neopentyl chloride, in 95% yield, is PPh3-CCl3CN." ... 

These reactions are most important for the preparation of acyl fluorides. " Acyl chlorides and anhydrides can be converted to acyl fluorides by treatment with polyhydrogen fluoride-pyridine solution" or with liquid HF at — 10°C. Formyl fluoride, which is a stable compound, was prepared by the latter procedure from the mixed anhydride of formic and acetic acids. Acyl fluorides can also be obtained by reaction of acyl chlorides with KF in acetic acid or with DAST. Carboxylic esters and anhydrides can be converted to acyl halides other than fluorides by the inorganic acid halides mentioned in 10-77, as well as with PhsPXa (X = Cl or but this is seldom done. Halide exchange can be carried out in a... 

Any of the four hydrogen halides can be added to double bonds.The compounds HI, HBr, and HF add at room temperature. The addition of HCl is more difficult and usually requires heat, although HCl adds easily in the presence of silica gel. The reaction has been carried out with a large variety of double-bond compounds, including conjugated systems, where both 1,2 and 1,4 addition are possible. A convenient method for the addition of HF involves the use of a polyhydrogen fluoride-pyridine solution.When the substrate is mixed with this solution in a solvent such as THF at 0°C, alkyl fluorides are obtained in moderate-to-high yields. 

Nitryl chloride (NO2CI) also adds to alkenes, to give p-halo nitro compounds, but this is a free-radical process. The NO2 goes to the less-substituted carbon. Nitryl chloride also adds to triple bonds to give the expected l-nitro-2-chloro alkenes. The compound FNO2 can be added to alkenes by treatment with HF in HNOa or by addition of the alkene to a solution of nitronium tetrafluoroborate (NOJBF4, see 11-2) in 70% polyhydrogen fluoride-pyridine solution (see also 15-37). 

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