Reaction end point

The rightmost structure is a weak complex of the products (having a binding energy of 1 kcal mol ), and for our purposes maybe construed as the reaction end point. 

Wiss [117] and Tumuluri [116] both determined the reaction end point and detected undesired side products or excessive intermediate concentration increases from spectra. Tumuluri went a step further, calculating the reaction kinetics for different catalysts to determine the most efficient and effective one. Interestingly, the reaction with one of the catalysts followed a different mechanism than the others examined. In one reaction, a long induction period was noticed and traced to an unanticipated side reaction. The structure of the side product could not be dehnitively determined because the MCR data reduction was too noisy, but its presence was clearly detected. Additional experiments specihcally designed to study that stage of the... 

Wenz and colleagues at Bayer Polymers Inc. describe the use of Raman spectroscopy to determine the reaction end point for the emulsion production of ABS graft copolymer [197]. Early termination reduces product yield and results in an extra product purification step termination too late reduces product quality. 

An alternative to univariate calibration is to use multivariate techniques to sense when a steady state has been reached in a chemical reaction. This approach has been successfully apphed to the detection of reaction end points [82]. A very similar technique can be used to establish deviation from steady state in a continuous process reactor. 

Objective determine reaction end point Off-line LC Agilent 1100 LC... 

Two procedures have been adopted to prevent oxidation of excess unreacted iodide by molecular oxygen. Either unreacted iodide is com-plexed with cadmium (Buege and Aust, 1978), or spectrophotometric measurements are made in air-free stoppered cuvettes and development of I3 is followed continuously. The second procedure allows reliable detection of the reaction end point and identifies any oxygen contamination (Hicks and Gebicki, 1979), but it is not applicable to routine measurements of many samples as the time taken for complete reduction of the hydroperoxide is prohibitive. Methods are therefore described which are based only on the procedure utilizing cadmium. 

Continuous fiow monitoring is inherently insensitive for direct judgment of reaction end points. In a typical coupling procedure with a fourfold excess of amino acid, absorbance drops from 4.00 to 3.05 or 3.01 units with 95 or 99% coupling, respectively. It is difficult to distinguish the approximate 1% difference between 3.05 and 3.01 accurately. In contrast, the 400% difference between 0.05 and 0.01 is easily measured when monitoring unreacted -amino groups. 

Advantages of this method are that 1) the electrolysis can be performed in neutral soln., 2) no supporting electrolyte is required, and 3) the reaction end-point is marked by cessation of the current. T. Iwasaki et al., Chem. Ind. 1973, 1163. 

The quantity of initiator employed varies between 0.2% - 4.0%, and may be of any of the types described earlier. The total process time varies between 8 and 30 hours with the reaction end point being greater than 99% conversion of monomer, as determined by... 

---