Crystallization adductive

R.A. Findlay, Adductive crystallization, in New Chemical Engineering Separatum Techniques (Schoen, Ed.), Wiley-Intersdence, New York, 1958. 

Somewhat similar are the so-called adductive crystallization processes, often (wrongly) called extractive crystallization, where reactions of complex/ adduct formation are used to separate compounds that are otherwise difficult to separate. Examples of adductive crystallization include separation of p- and m-cresols (137), separation of o- and p - n i troch I oro ben zcn cs (138), separation of quinaldine and isoquinoline (139), separation of nonaromatic compounds from naphtha-cracking raffinate (140), and separation of p-cresol from 2,6-xylenol (141). Other examples of reactive crystallization/precipitation reported in the literature are listed in Table 5. 

Figure 5.7 X-ray crystal structure projections of copper-catecholate adducts obtained by Comba and co-workers [41] (a, c and d), and x-ray crystal structure of one of the dicopper(ll)-catecholate adducts crystallized by Meyer and coworkers (b) [42],...

Attempts to structurally characterize the generated Ln(III)/Al hetero-bimetallic complexes were not successful. Addition of coordinating solvents, such as THF or pyridine, afforded complex mixtures from which only lanthanide(III) chloride donor-adducts crystallized. The presence of reactive ethyl groups was confirmed by the reaction with D20 (generating CH3CH2D) [134], The catalytic relevance of such heterobimetallic complexes was confirmed by the quantitative conversion of a 7500-fold excess of iso-prene into polyisoprene within 5-10 minutes at ambient temperature, after the addition of one equivalent of i-Bu3Al cocatalyst. 

Description In the bisphenol reaction section (1), acetone is reacted with excess phenol in multiple fixed-bed reactors, containing a DOWEX resin catalyst, to form BPA and water. The outlet from the reactors is fed to the adduct crystallizers (2) where a crystal adduct... 

The submitters report that a two-stage exotherm occurs during the addition. The first exotherm occurs as the trimethylboroxine reacts with the diphenylprolinol, and the second occurs as the intermediate bismethylboronic acid adduct crystallizes. Typically, the intermediate begins to crystallize after ca. one third of the trimethylboroxine is added. The reaction should not be run more concentrated. The checkers observed an exothermic reaction (warming from 20 to 45°C) after approximately one half to two thirds of the trimethylboroxine/THF solution was added. 

Since these bisulfite addition compounds are ionic water-soluble compounds and can be formed in up to 90% yield, they serve as a useful means of separating aldehydes and methyl ketones from mixtures of organic compounds. At high sodium bisulfite concentrations these adducts crystallize and can be isolated by filtration. The aldehyde or ketone can be regenerated by adding either a strong acid or base ... 

When the intermolecular forces are relatively strong and directional, crystalline molecular compounds (crystalline molecular complexes) are formed. They have fixed stoichiometries and ordered structures. These two-component molecular crystals are also called cocrystals or maybe adduct crystals. Hydrogen-bonded cocrystals, donor-acceptor crystals (charge transfer crystals), and inclusion crystals (host-guest crystals) are examples of crystalline molecular complexes. Crystalline organic salt is a special case of hydrogen-bonded cocrystal or donor-acceptor crystal, i.e., proton (or electron) transfer from the acid (or donor) to base (or acceptor) occurred. 

A -Alkylcarbazoles formed yellow to orange to deep brown 1 1 charge transfer crystals with wi-dinitrobenzene, 3,5-dinitrobenzoic acid (3,5-DNBA) and its derivatives (Scheme 30) [57]. On the other hand, attempts to obtain adduct crystals of A -alkylcarbazoles with o- or p-dinltrobenzene and with 2,4- or 3,4-dinitrobenzoic acid failed. Upon solid-state photolysis, many of these adduct crystals underwent photoredox reactions and e a position of the A -alkylcarba-zoles was oxidized to produce carbazole, JV-acylcarbazoles, and A/-(hydroxy-... 

The diones and aldehydes whose photoreactions have been reported are summarized in Table 5 where it can be seen that this system has been investigated almost to excess. Most of the quinone reactions were performed in Cairo sunlight using benzene solutions of quinone containing a moderate excess of aldehyde. The adducts crystallized from solution usually in good to excellent yield no attempts were made to analyze the total reaction product. With one exception, all quinone adducts are products of 1,4-addition both cyclic 146> and open-chain 83> tautomeric structures have been proposed for these enediol monoesters. Infrared... 

Monoisopinocampheylborane of essentially 100% ee is best prepared from diisopinocampheylborane84. Treatment of one equivalent of diisopinocampheylborane with TMEDA provides a diamine/monoisopinocampheylborane (1/2) adduct with the liberation of one equivalent of a-pinene. The adduct crystallizes in enantiomerically pure form. Free monoisopinocampheylborane is liberated by treatment with a boron trifluoride-diethyl ether complex. The di-amine/boranc (1/2) adduct is highly insoluble and precipitates quantitatively. 

It is open to question whether adduct formation can really be considered as a true crystallization process, but the methods of operation employed are often indistinguishable from conventional crystallization methods. Several different names have been given to separation techniques based on the formation of adducts, but the name adductive crystallization is probably the best and will be used here. 

Several possible commercial apphcations of adductive crystallization have been reported. For example, the system m-cresol-p-cresol forms two eutectics over the complete range of composition, and the separation of the pure components cannot be made by conventional crystallization. Savitt and Othmer (1952) described the separation of mixtures of these two components by the use of benzidine to form a sohd addition compound with p-cresol. Actually both m-cresol and p-cresol form addition compounds with benzidine, but the meta-compound melts at a lower temperature than the para-. If the process is carried out at an elevated temperature the formation of the meta- complex can be avoided. The method consists of adding benzidine to the meta-para- mixture at 110 °C. The /7-cresol benzidine crystallizes out, leaving the m-cresol in solution. The crystals are filtered off, washed with benzene to remove w-cresol, and the washed cake is distilled under reduced pressure to yield a 98 per cent pure i-cresol. 

As described above, adductive crystallization is one method for separating a binary eutectic mixture into its component parts. Another possibility is to alter the solid-liquid phase relationships by introducing a third component, usually a liquid called the solvent. This process is known by the name extractive crystallization . 

Jadhan, V.K., Chivate, M.R. and Tavare, N.S. (1991) Separation of p-cresol from its mixture with 2,6 xylene by adductive crystallization. Chemical Engineering Data, 36, 249-251. 

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