Colourless steps

Mechanisms ascribed to class 2 can be called those with "colourless steps (i.e. those containing no observed substances). 

H2N (CH2)a NH2- Colourless solid when pure m.p. 4LC, b.p. 204 C. Manufactured by the electrochemical combination of two molecules of acrylonitrile to adiponitrile followed by catalytic reduction, or by a series of steps from cyclohexanone via adipic acid. Used in the production of Nylon [6, 6]. 

Phenol condenses with phthahc anhydride in the presence of concentrated sulphuric acid or anhydrous zinc chloride to yield the colourless phenolphthalein as the main product. When dilute caustic alkah is added to an alcoholic solution of phenolphthalein, an intense red colouration is produced. The alkali opens the lactone ring in phenolphthalein and forms a salt at one phenolic group. The reaction may be represented in steps, with the formation of a h3q)othetical unstable Intermediate that changes to a coloured ion. The colour is probably due to resonance which places the negative charge on either of the two equivalent oxygen atoms. With excess of concentrated caustic alkali, the first red colour disappears this is due to the production of the carbinol and attendant salt formation, rendering resonance impossible. The various reactions may be represented as follows ... 

It will noticed that the initial steps correspond with those used in the manufacture of glycerol. The material is available commercially at 98% purity and is a colourless mobile liquid. 

If the metallisable dye is insoluble in water, a miscible solvent such as ethanol or ethylene glycol may be added. Polar solvents such as formamide or molten urea have sometimes been preferred. It is likely that such solvents will preferentially displace water molecules and coordinate with the chromium (III) ion as the first step in the reaction. If colourless organic chelates of chromium, such as those derived from oxalic or tartaric acid, are used instead of or in addition to hydrated chromium (III) salts, the difficulty of replacing the strongly coordinated water molecules in the first stage of the reaction is eliminated. In this way the initial reaction can be carried out at high pH without contamination by the precipitation of chromium hydroxide. Use of the complex ammonium chromisalicylate (5.12) in this connection should also be noted (section 5.4-1). 

Since we believed that the cations of this electrolyte include the polyisobutylium ion, it was an obvious next step to test whether the corresponding tert-butylium salt is also stable under these conditions. The question was tested by breaking a phial of carefully purified tert- mty bromide into a solution of AlBr3 in methyl bromide at -78 °C the mole ratio of the reagents was 1. The introduction of the tertiary halide produced a rapid increase in conductivity which became stable after approximately 10 minutes and remained thus the solution was colourless throughout. Its concentration was varied as described above and the resultant conductivity change is shown in Figure 10. 

Although the synthesis appears to be very straightforward, it is actually very difficult to obtain a colourless liquid, as trace amounts of impurities lead to discolouration. The first step of the reaction does not go to completion and the... 

A similar study has been carried out in order to test the capacity of RP-HPLC for the authenticity test of chilli powders on the basis of pigment composition. Carotenoid pigments were extracted by shaking 3 g of chilli powder with 10 ml of acetone for 30 min. The supernatant was decanted and the procedure was repeated as the solid rest was nearly colourless. The collected organic phases were evaporated and redissolved in the mobile phase. Separations were performed on a narrow-bore ODS column (150 X 2 mm i.d., carbon loading, 9.5 per cent). Eluents A and B were methanol-ACN (80 20, v/v) and bidistilled water, respectively. Gradient elution was initiated by 15 per cent A increased to 80 per cent A in 25 min, held for 10 min, increased to 90 per cent A in 10 min, held for 10 min, increased to 97 per cent A in 3 min and held for 62 min. Each step of gradient elution was linear. Measurements were... 

Kai Pii is formed quantitatively from Na3p7 and Pi (in en) in a well defined reaction. The colourless solvate Uai Pii 6en can be obtained from en in crystalline form by counter-current diffusion of THF (Figure 5)- Again we find a solvated molecule or ion-complex Nai Pii in the crystal. The polyanion Pi ", whose trimethyl-silyl substituted derivatives have already been observed in small quantities in mass-spectra ( ), constitutes the first methodically executed step to an oligomerization and finally to a complete polymerization of Pv clusters (I6). 

Equations of type (97) can also comprise a summand including concentrations of the whole of the brutto-reaction participants, i.e. K g [CH4][H20]-[CO][H2]3. It is evident that, in this case, the reaction mechanism must be attributed to class 2 and contains a sufficiently large number of "colourless reactions. The number of steps here amounts to s > nin + nprod. The analysis performed using this example can readily be generalized. For a one-route catalytic reaction with one-route linear mechanism the following conclusions can be drawn. 

The steps of water production can be treated as reversible since there are terms containing [H20]. But as there is no term with [H20]2, it is evident that these two steps are separated by some irreversible step. If s = 4, every one of the terms in the denominator of eqn. (101) must be a product of three reaction weights. The terms [HJ2 and / 2[H2][02] are sure to contain a weight of the "colourless reaction since their exponential factor is two. This is still more valid at s = 5, when these terms will include the weights of two "colourless reactions. 

The mechanism suggested has five steps including two "colourless reactions [steps (2) and (4)]. Note that to interpret data it would be useful to have information concerning the temperature dependence of the complexes. One can say in advance that K and Kl are the Arrhenius complexes, whereas K2... 

R-(+)-l,2,4-butantriol (0.7 g, 6.6 mmol), prepared as described in step (a) above, was stirred for 1.5 hr in acetone (50 ml) containing 3 drops of cone, perchloric acid a satured solution of sodium bicarbonate in water (5 ml) was added and the stirring was continued for additional 10 min. The precipitate was filtered off and the filtrate evaporated under reduced pressure [2.7 kPa,(20 mm Hg), 30°C], The residue was taken up in ethyl acetate, washed with satured aqueous sodium bicarbonate (5 ml) and brine (5 ml), and dried over magnesium sulfate. Evaporation of the solvent and distillation gave the title compound as a colourless oil (0.3 g, 2.05 mmol, 31%) b.p. 104°-106°C/20 mm Hg nD2°=1.4390. 

This step depolymerizes the chain of linkers yielding restriction fragments containing single EcoRl sticky ends at both termini. Before cloning these fragments it is important to remove, as completely as possible, the depolymerized linkers since these would also efficiently ligate into the vector and yield colourless recombinant plaques. Since the vast majority of the restriction... 

Wash on a sintered glass filter funnel the product diamide with further portions of toluene (2 x 10 mL) and then chloroform (5x5 mL). Dry the solid residue under high vacuum (0.1 mmHg, 2 h) to give a colourless solid, m.p. 196-7°C, 14.7 g, 76%. Use this diamide directly in the following step without further purification. 

The slower running material from the preparative thin layer chromatography plate (flf = 0.4) corresponds to the 2 2 cyclic adduct, that is, the desired 18-crown-6 derivative, 1,T,4,4 -tetra-0-benzyl-2,2 3,3 -oxydi-ethylenedi-L-threitol ll-1. Removal and isolation of this material from the silica (remember, caution, mask necessary when using silica) as in steps 14 and 15 for the smaller crown, affords a colourless oil ll-1 (274 mg, 11%), [a]D +5.8° (c = 3.5, chloroform). 

Heat and stir the mixture at 100°C for 14 h, whereupon a precipitate of the product phosphonium salt will form. Let the flask cool to ambient temperature, filter the suspension over a Buchner funnel, and wash the crude solid repeatedly with 100 ml portions of hot toluene to remove residual tri-phenylphosphane. Dry the product in vacuo at 100°C to obtain a crystalline colourless solid, m.p. 207°C, 23 g (97%). It is sufficiently pure for the next step, but may be recrystallized from chloroform/acetone. 

For isolation of la, filter the suspension, which should be once again almost colourless, on a Buchner funnel and wash the remaining solid with ether. Recrystallize it first from minimum amount of water, and then from chloroform/acetone mixtures to obtain pure 1a, m.p. 271°C, 7.5 g (94%). For the preparation of 2, the ethereal suspension resulting from step 4 can be used right away. 

To the colourless suspension of la resulting from step 4 add another 22 mmol of phenyl-lithium by means of a syringe. Stir the mixture for a couple of minutes, then remove the condenser altogether and, under a strong stream of nitrogen, add benzaldehyde (2.2 g, 20 mmol) to the red solution. 

A simple example of an intramolecular Lewis acid/base reaction (thus avoiding the association step) is the xanthene dye rhodamine B, which exists in solution either in the red-coloured zwitterionic form (26a) or as the colourless lactonic form (26b) [175, 221, 222]. Solutions of rhodamine B in non-HBD solvents such as dimethyl sulfoxide,... 

The above phenylformamidinc (2.1 g) (note the crude product can also be used in the cyclization step) is warmed in a sodium cthoxide solution made by dissolving sodium (0.5 g) in ethanol (15 ml). All of the phenylformamidinc dissolves in 3-5 min.. After 15min a 2- 3-fold volume of water is added to the solution, which is allowed to stand (1 h) to crystallize. Recrystallization from ethanol gives nearly colourless crystals (1.8 g, 85%), m.p. 97-99 C. 

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