Extent of amine reaction

Epoxy Cure Time (min.) A PP Cure PS Product SS T s %) ST t Extent of Amine Reaction... 

The overall extent of amine reaction ) as defined before can now... 

Figure 2. Experimental composition of cure species as a function of extent of amine reaction for DGEB-DDS. Refer to Scheme I for definitions of cure species. Two dotted lines show predictions for reactivity of ratio of either 0.1 or 1. (Reproduced from Ref. 4. Copyright 1986 American Chemical Society.)...

In order to correlate fluorescence intensity at 565 nm with the overall extent of amine reaction, we plotted Ip versus in Fig. 6, for both epoxies cured at three isothermal cure temperatures. In this figure, 5 is estimated from the deconvolution of UV-visible spectra. All -fhe data fall on a single smooth curve whose slope is much sharper at later stages of cure especially after gelation. In other words, fluorescence Intensity constitutes a sensitive gauge for monitoring cure beyond gelation, because it derives mostly from tertiary amine products. 

At this point, the anaiyte may not be amenabie to UV, FL, or EC detection. In this case, the best course of action may be to choose LC/MS (see Section 4.2). However, one other option is to use a pre- " or post-coiumn derivatization step to increase the detectabiiity of the anaiyte with respect to FL or UV. Fluorescent or UV labels are available for carboxylic acids," amines, phenols, and thiols. The decision to use pre- or post-column derivatization is predicated upon the functionality of the analyte available for derivatization and the rate and extent of the reaction between each derivatizing agent and the analyte. 

The same procedure is used for the formation of resins 2 and 8 by reaction of the nitroarenes with the resin-bound [3-alanine or mercaptan/ amine linker, respectively. The o-fluoronitroarenes (Fig. 3) are dissolved in DMSO or NMP (at a concentration between 1.5 and 2 M) and added to the resin, followed by diisopropylethylamine (10 equivalents) and additional DMSO or NMP (if required) to ensure resin solvation. Although many nitroarenes react rapidly at room temperature, in a library format the resin/nitroarene mixture is heated overnight at 50° to help achieve equivalent reaction kinetics between different monomers. Under the same conditions, some o-chloronitroarenes are synthetically useful. The extent of the reaction can be assessed qualitatively (or quantitatively, if desired) by carrying out a ninhydrin test to check for the presence of free amine. In any case, the resins are acetylated with five equivalents of acetic anhydride/pyridine/DMF (1 1 10) for 20 min to cap any unreacted amine. 

Under substitution conditions, amines proceed all the way to form quaternary salts, which makes it difficult to control the extent of the reaction. 

The rate of reaction of ozone with amine was determined during the ozonization of rubber solution, where the reaction between ozone and rubber also proceeded concurrently. The extent of the reaction of rubber with ozone was calculated from the change in unsaturation of the rubber determined by the Wijs reagent. For example, SBR (Japan Synthetic Rubber, JSR 1502), purified by precipitation with acetone from benzene solution, was dissolved in carbon tetrachloride to give a 5% rubber solution. The rubber solution (20 ml.) was added with 80 ml. of carbon tetrachloride containing 1 X 10 3 mole of amine derivatives. Oxygen, containing 0.89% ozone, was introduced into the solution at 30°C. for 3 minutes at the rate of 550-560 ml./min. Under these conditions, all... 

Ethylene and Propylene Oxide Amine Adducts. Polyamines, such as DETA, react readily with ethylene oxide in the presence of water to yield mono- or dihydroxyalkyl derivatives, depending on the ratio of reactants. As the extent of the reaction progresses, the resulting... 

Cross-Linking Reactions of Polymers. Bisdichloromaleimide-amine polymers contain (a) a double bond in the maleimidyl group, (b) chlorine, and (c) secondary amine group (-NH-). It may be possible to cross-link them either by the opening of the double bond (thermal polymerization) or by the nucleophilic displacement of chlorine by the secondary amine. The representative reaction scheme for such reactions is shown in Figure 6. The extent of such reactions may be evaluated by solubility measurements in dimethyIformamide. 

To control the extent of chemical reactions between the metallic surface and liquid monomers, leading to the formation of a thick interphase, liquid epoxyamine mixtures were kept in contact with the metallic surface at room temperature for various periods of time before the desired adhesive curing cycle was started (e.g., see Pig. 7.1) at 190 °C, vitrification appeared within a few minutes, stopping any reaction between amine and metal, and/or diffusion phenomenon. These curing cycles allowed the maximum conversion (i.e., the maximum glass transition temperature). Gonversely, when interphase formation was not desired. 

Attack of the carboxyl-component on the O-acylisourea intermediate is facile, unimpeded by the polymer. In fact, the symmetrical anhydride can first be generated in solution and if desired DCU removed prior to the addition of the acylating mixture to the resin-bound amine-component. In this mode of coupling the lifetime of the overly reactive O-acylisourea is significantly reduced with the simultaneous reduction in the extent of side reactions such as N-acyl-urea formation. The symmetrical anhydride approach, considered earlier as too expensive, became with the decrease in price of Boc-amino acids quite popular in recent years. 

This accelerating behavior appears similar to the autoaccderation phenonomen observed for the 8 2 addition due to the initiation reaction (Rxn. 36), yet there are substantial and fundamental differences between the two phenomena. First, in the autoaccelerating reaction the increasing active catalyst concentration is directly proportional to the extent of epoxy reaction. This is not the case for the epoxy-phenol reaction. The active complex formation reaction, Rxn. 36, is independent of the propagation reaction, Rxn. 37. thus, any observed proportionali is simply coincidental. Second, the rate of production of active catalytic complex will decrease as the tertiaiy amine or phosphine is consumed in Rxn. 36. The maximum concentration of active catalytic complex is limited by the initial charge of catalyst. These considerations are not accounted for in the autoacceleration model. 

The very high reactivity of the P—Cl bonds in (4) forms the basis for the now well-known macromolecular substitution method, which has been used to synthesize polymers of types (1) and (2) and some polymers that are hybrids of these and (3). The method involves nucleophilic reactions of (4), and to some extent of its difluoro analogue, with alkoxides or amines. 

AnUine, however, is too toxic for use in mbber products. Its less toxic reaction product with carbondisulfide, thiocarbanihde, was introduced as an accelerator in 1907. Further developments led to guanidine accelerator [4]. Reaction products formed between carbon disulfide and aliphatic amines (dithiocarbamates) were first used as accelerators in 1919 [5]. These were and still are the most active accelerators in respect to both cross-finking rates and extent of cross-link formation. However, most dithiocarbamates accelerators give little or no scorch resistance and therefore cannot be used in aU applications. 

Very significant acceleration in the rate of deprotonation of 2-methylcyclohexanone was observed when triethylamine was included in enolate-forming reactions in toluene. The rate enhancement is attributed to a TS containing LiHMDS dimer and triethylamine. Steric effects in the amine are crucial in selective stabilization of the TS and the extent of acceleration that is observed.18... 

In an early work by Mertz and Pettitt, an open system was devised, in which an extended variable, representing the extent of protonation, was used to couple the system to a chemical potential reservoir [67], This method was demonstrated in the simulation of the acid-base reaction of acetic acid with water [67], Recently, PHMD methods based on continuous protonation states have been developed, in which a set of continuous titration coordinates, A, bound between 0 and 1, is propagated simultaneously with the conformational degrees of freedom in explicit or continuum solvent MD simulations. In the acidostat method developed by Borjesson and Hiinenberger for explicit solvent simulations [13], A. is relaxed towards the equilibrium value via a first-order coupling scheme in analogy to Berendsen s thermostat [10]. However, the theoretical basis for the equilibrium condition used in the derivation seems unclear [3], A test using the pKa calculation for several small amines did not yield HH titration behavior [13],... 

---