Direct DPC process

The history of direct DPC process development at GE can be considered as a case study. In the mid-1970s. Chalk discovered that /rara-substituted phenols can be oxidatively carbonylated using stoichiometric amounts of a Ru, Rh, Os, Ir, or Pd salt, from which the palladium salts were the most active (Eq. (12.3)) [5]. Yields of carbonylation products were high, but the reaction yielded 1 mol of Pd° for every mole of product, so it was stoichiometric [6]. In the late 1970s, Hallgren and Matthews assumed that DPC was formed by reductive elimination from the acyl Pd(ll) carbonyl complex [7]. 

However, DPC yield and Pd turnover number (Pd TON defined as mol DPC/mol Pd charged) obtained in early works remained low. Unlike aliphatic alcohols, the oxidative carbonylation of aromatic alcohols is difficult due to their increased acidity and oxidative instability. They, therefore, require expensive catalysts [7]. It was the high cost of the optimal Pd-based catalysts, which were superior compared with all others, and low reaction rates that prevented the direct DPC process from being commercially viable. 

The use of an inert stripping agent such as pentane vapor for the removal of water from a direct DPC process was claimed [85]. Pentane was condensed to separate from the water stripping step and recycled back to the water stripping step [85]. 

The author thanks the members of the GE team who worked with him on the direct DPC process Dick Battista, Peter Bonitatibus Jr., Michael Brennan, James... 

For example, in the photolysis of (30) in toluene solution, the product of insertion of DPC into the benzylic C—H bonds, 1,1,2-triphenylmethane (31), was accompanied by substantial amounts of 1,1,2,2-tetraphenylethane (32) and bibenzyl (33).When solvents such as cyclohexane are used, tetraphenylethane (32) is formed as the major product, indicating that direct C—H insertion in the singlet state is not the main process in most diarylcarbenes (Scheme 9.7). ° In contrast, 9-cyclohexylfluorene (37) is produced by photolysis of diazofluorene (36) in cyclohexane as a main product (65%) along with a small amount of escaped products (38 and 39). One can estimate in this case that at most 14% of 37 arises from free radical processes. Similarly, direct or sensitized photolysis of diazomalonate in 2,3-dimethylbutane gives C—H insertion products, but in the triplet-sensitized... 

Differential Photocalorimetry (DPC) (19.201. The polymerization being an exothermal process, the reaction can be monitored in real time by differential scanning calorimetry (DSC). From the recorded thermogram which shows the variation of the heat flow with the irradiation time, the rate of polymerization can be directly calculated, provided the standard heat of polymerization (AHq) is known. For acrylic monomers, AHg values are usually in the range of 78 to 86 kJ mol depending on the monomer considered. 

Fig. 4 PLA production processes (1) direct polycondensation (DPC) of lactic add and (2) ringopening polymerization (ROP) of lactide...

DPC also measures reaction rate and the effects of processing conditions on photospeed providing direct information for determining optimnm processing conditions including exposure time, temperature, wavelength, intensity, and atmospheric environment. 

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