Indicators reaction + amines

Here we shall confine ourselves to the solvents benzene and 1,2-dichloroethane (class 8). Considering benzene, many investigators have demonstrated since the 1930s the feasibility of titrations in this solvent using both potentiometric and spectrophotometric methods, paying much attention to acid-base indicator reactions under the influence of primary, secondary and tertiary amines. Association of carboxylic acids in benzene was studied at a later stage, mainly on the basis of colligative properties, IR spectroscopy and solvent extraction. ... 

In the case of primary aliphatic amines, the reaction products are dramatically affected by the solvent employed. For instance, in the presence of solvents apt to produce a specific solvation of amines (chloroform, and an amine chlorohydrate solution in methylene dichloride), the reaction with hexachloride precursors terminates to yield the trisubstituted product DD D" formed via route A. At the same time, the use of some other solvents (such as benzene, 1,4-dioxane, THF, methylene dichloride, DMF, and alcohols, or the corresponding amine media) led to the formation of the sole tetrasubstituted product (DD"D"). In addition, in the case of sterically unhindered primary amines an alternative isomer (D D D") is not isolated, which indicates reaction route A and a specific control of the tie reaction in the transition state by solvation interactions and intramolecular hydrogen bonds. In the case of the dichloride FeBd2(C12Gm)(BF)2 precursor, with both primary (cyclohexylamine) and secondary (diethylamine and piperazine) aliphatic amines, only a monosubstituted product of the Bd2D type is formed in chloroform, whereas in some other solvents, a diamine clathrochelate of the Bd2D" type is obtained with both sterically hindered and unhindered primary aliphatic amines. 

The catalytic fluorimetric determination of Mn2+ and Fe3+ using the oxidation of 2-hydroxybenzaldehyde thiosemicarbazone by hydrogen peroxide in the presence of amines as the indicator reaction [47]. 

Catalysts will not only accelerate reaction rates but may also change the order of reactivity. Table 3 illustrates this behavior. These data indicate that amines do not affect the relative reactivities of different isocyanates and show that Zn, Fe, and Co complexes actually raise the reactivity of aliphatic isocyanates above aromatic isocyanates. 

Dissolve 0-5 g. of the substance in 10 ml. of 50 per cent, alcohol, add 0-5 g. of solid ammonium chloride and about 0 -5 g. of zinc powder. Heat the mixture to boiling, and allow the ensuing chemical reaction to proceed for 5 minutes. Filter from the excess of zinc powder, and teat the filtrate with Tollen s reagent Section 111,70, (i). An immediate black or grey precipitate or a silver mirror indicates the presence of a hydroxyl-amine formed by reduction of the nitro compound. Alternatively, the filtrate may be warmed with Fehling s solution, when cuprous oxide will be precipitated if a hydroxylamine is present. Make certain that the original compound does not aflfect the reagent used. 

The experimental conditions necessary for the preparation of a solution of a diazonium salt, diazotisation of a primary amine, are as follows. The amine is dissolved in a suitable volume of water containing 2 5-3 equivalents of hydrochloric acid (or of sulphuric acid) by the application of heat if necessary, and the solution is cooled in ice when the amine hydrochloride (or sulphate) usually crystallises. The temperature is maintained at 0-5°, an aqueous solution of sodium nitrite is added portion-wise until, after allowing 3-4 minutes for reaction, the solution gives an immediate positive test for excess of nitrous acid with an external indicator—moist potassium iodide - starch paper f ... 

It has been tentatively suggested that one mechanism underlies the Willgerodt reaction and the Kindler modification of it. A labile intermediate is first formed which has a carbon—carbon bond in the side chain. The scheme is indicated below it postulates a series of steps involving the addition of ammonia or amine (R = H or alkyl), elimination of water, re addition and eUmination of ammonia or amine until the unsaturation appears at the end of the chain then an irreversible oxidation between sulphur and the nitrogen compound may occur to produce a thioamide. 

Benzenesulphonyl chloride test. Proceed as in the benzoyl chloride test, but use 15-20 ml. of 5 per cent, sodium hydroxide solution. Examine the product when the odour of the sulphonyl chloride has disappeared. (If no reaction has occurred, the substance is probably a tertiary amine.) If a precipitate appears in the alkaline solution, dilute with about 10 ml. of water and shake if the precipitate does not dissolve, a secondary amine is indicated. If the solution is clear, acidify it cautioiosly to Congo red with dilute hydrochloric acid a precipitate is indicative of a primary amine. 

Note that for 4.42, in which no intramolecular base catalysis is possible, the elimination side reaction is not observed. This result supports the mechanism suggested in Scheme 4.13. Moreover, at pH 2, where both amine groups of 4.44 are protonated, UV-vis measurements indicate that the elimination reaction is significantly retarded as compared to neutral conditions, where protonation is less extensive. Interestingy, addition of copper(II)nitrate also suppresses the elimination reaction to a significant extent. Unfortunately, elimination is still faster than the Diels-Alder reaction on the internal double bond of 4.44. 

The desired pyridylamine was obtained in 69 % overall yield by monomethylation of 2-(aminomethyl)pyridine following a literature procedure (Scheme 4.14). First amine 4.48 was converted into formamide 4.49, through reaction with the in situ prepared mixed anhydride of acetic acid and formic acid. Reduction of 4.49 with borane dimethyl sulfide complex produced diamine 4.50. This compound could be used successfully in the Mannich reaction with 4.39, affording crude 4.51 in 92 % yield (Scheme 4.15). Analogous to 4.44, 4.51 also coordinates to copper(II) in water, as indicated by a shift of the UV-absorption maximum from 296 nm to 308 nm. 

The "zip-reaction (U. Kramer, 1978, 1979) leads to giant macrocycles. Potassium 3- ami-nopropyl)amide = KAPA ( superbase ) in 1,3-diaminopropane is used to deprotonate amines. The amide anions are highly nucleophilic and may, for example, be used to transam-idate carboxylic amides. If N- 39-atnino-4,8,12,16,20,24,28,32,36-nonaazanonatriacontyl)do-decanolactam is treated with KAPA, the amino groups may be deprotonated and react with the macrocyclic lactam. The most probable reaction is the intramolecular formation of the six-membered ring intermediate indicated below. This intermediate opens spontaneously to produce the azalactam with seventeen atoms in the cycle. This reaction is repeated nine times in the presence of excess KAPA, and the 53-membered macrocycle is formed in reasonable yield. 

Reaction (5.N) describes the nylon salt nylon equilibrium. Reactions (5.0) and (5.P) show proton transfer with water between carboxyl and amine groups. Since proton transfer equilibria are involved, the self-ionization of water, reaction (5.Q), must also be included. Especially in the presence of acidic catalysts, reactions (5.R) and (5.S) are the equilibria of the acid-catalyzed intermediate described in general in reaction (5.G). The main point in including all of these equilibria is to indicate that the precise concentration of A and B... 

This polymerization is carried out in the two stages indicated above precisely because of the insolubility and infusibility of the final product. The first-stage polyamide, structure [IX], is prepared in polar solvents and at relatively low temperatures, say, 70°C or less. The intermediate is then introduced to the intended application-for example, a coating or lamination-then the second-stage cyclization is carried out at temperatures in the range 150-300°C. Note the formation of five-membered rings in the formation of the polyimide, structure [X], and also that the proportion of acid to amine groups is 2 1 for reaction (5.II). 

Trilialophenols can be converted to poly(dihaloph.enylene oxide)s by a reaction that resembles radical-initiated displacement polymerization. In one procedure, either a copper or silver complex of the phenol is heated to produce a branched product (50). In another procedure, a catalytic quantity of an oxidizing agent and the dry sodium salt in dimethyl sulfoxide produces linear poly(2,6-dichloro-l,4-polyphenylene oxide) (51). The polymer can also be prepared by direct oxidation with a copper—amine catalyst, although branching in the ortho positions is indicated by chlorine analyses (52). 

Amines can also swell the polymer, lea ding to very rapid reactions. Pyridine, for example, would be a fairly good solvent for a VDC copolymer if it did not attack the polymer chemically. However, when pyridine is part of a solvent mixture that does not dissolve the polymer, pyridine does not penetrate into the polymer phase (108). Studies of single crystals indicate that pyridine removes hydrogen chloride only from the surface. Kinetic studies and product characterizations suggest that the reaction of two units in each chain-fold can easily take place further reaction is greatiy retarded either by the inabiUty of pyridine to diffuse into the crystal or by steric factors. 

The hterature suggests that more than one mechanism may be operative for a given antiozonant, and that different mechanisms may be appHcable to different types of antiozonants. All of the evidence, however, indicates that the scavenger mechanism is the most important. All antiozonants react with ozone at a much higher rate than does the mbber which they protect. The extremely high reactivity with ozone of/)-phenylenediamines, compared to other amines, is best explained by their unique abiUty to react ftee-tadicaHy. The chemistry of ozone—/)-PDA reactions is known in some detail (30,31). The first step is beheved to be the formation of an ozone—/)-PDA adduct (32), or in some cases a radical ion. Pour competing fates for dissociation of the initial adduct have been described amine oxide formation, side-chain oxidation, nitroxide radical formation, and amino radical formation. 

All the aminoisothiazoles are normal weak amines. The 3- and 5-amino compounds can theoretically exist in tautomeric forms, but their reactions indicate that the amino forms... 

The esterification reaction may be carried out with a number of different anhydrides but the literature indicates that acetic anhydride is preferred. The reaction is catalysed by amines and the soluble salts of the alkali metals. The presence of free acid has an adverse effect on the esterification reaction, the presence of hydrogen ions causing depolymerisation by an unzipping mechanism. Reaction temperatures may be in the range of 130-200°C. Sodium acetate is a particularly effective catalyst. Esterification at 139°C, the boiling point of acetic anhydride, in the presence of 0.01% sodium acetate (based on the anhydride) is substantially complete within 5 minutes. In the absence of such a catalyst the percentage esterification is of the order of only 35% after 15 minutes. 

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