More Recent Work

Particle types Specific charge (pC/kg) Method Source 

Suspended Probe Measurements Revisited. One group has explored the use of suspended probes to gain more useful qualitative electrostatic data in fluidized beds by developing a capacitive circuit model forthe bed (Rojo etal., 1986). Open-circuit voltages induced on immersed 

In general, the data of Table 4 tend to confirm this estimated range however, the upper limit of 1.0 pC/kg is considerably exceeded in the case of data obtained with individual particles of tribo-active, insulating polymers. Whether or not significant volume separation of positive and negative charges occurs with these polymers is not known. Thus, the validity of the upper limit in Eq. (9) is difficult to judge. 

Binary mixtures of glass ballotini and steel beads of nearly equal size (-500 pm and -275 pm, respectively) also exhibit reduced electrostatic activity, as measured by suspended electrodes (Guardiolaet al., 1992). The highly conducting steel beads were added to the glass particles in amounts up to approximately 10% by volume. 

The obvious measures of lowering superficial gas velocity in the bed and the selection of wall and/or particulate materials certainly exist. But, in a given process, there is often no practical way to implement such solutions. Fluidization conditions are dictated by the application for which the bed is intended furthermore, the choice of particulate materials can seldom be made on the basis of electrostatic considerations. 

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Gilman [124] and Westwood and Hitch [135] have applied the cleavage technique to a variety of crystals. The salts studied (with cleavage plane and best surface tension value in parentheses) were LiF (100, 340), MgO (100, 1200), CaFa (111, 450), BaFj (111, 280), CaCOa (001, 230), Si (111, 1240), Zn (0001, 105), Fe (3% Si) (100, about 1360), and NaCl (100, 110). Both authors note that their values are in much better agreement with a very simple estimate of surface energy by Bom and Stem in 1919, which used only Coulomb terms and a hard-sphere repulsion. In more recent work, however, Becher and Freiman [126] have reported distinctly higher values of y, the critical fracture energy. ... 

SERS. A phenomenon that certainly involves the adsorbent-adsorbate interaction is that of surface-enhanced resonance Raman spectroscopy, or SERS. The basic observation is that for pyridine adsorbed on surface-roughened silver, there is an amazing enhancement of the resonance Raman intensity (see Refs. 124—128). More recent work has involved other adsorbates and colloidal... 

Two other examples will sufhce. Methane physisorbs on NaCl(lOO) and an early study showed that the symmetrical, IR-inactive v mode could now be observed [97]. In more recent work, polarized FTIR rehection spectroscopy was used to determine that on being adsorbed, the three-fold degeneracies of the vs and v modes were partially removed [98]. This hnding allowed consideration of possible adsorbate-adsorbent geometries one was that of a tripod with three of the methane hydrogens on the surface. The systems were at between 4 and 40 K so that the equilibrium pressure was very low, about 10 atm. 

The literature of surface diffusion is now quite extensive. A review of the basic ideas, with reference to many of the earlier papers, is given by Dacey [44], and a good selection of references including more recent work can be found in Aris [45]... 

Articles fabricated from FEP resins can be made bondable by surface treatment with a solution of sodium in Hquid ammonia, or naphthalenyl sodium in tetrahydrofuran (64) to faciUtate subsequent wetting. Exposing the surface to corona discharge (65) or amines at elevated temperatures in an oxidizing atmosphere (66) also makes the resins bondable. Some of the more recent work is described in References 67—69. 

More recent work reports the onset of thermal degradation at lower temperatures and provides a clearer picture of the role of oxygen (73—75). In the presence of oxygen, backbone oxidation and subsequent cleavage reactions initiate decomposition. In the absence of oxygen, dehydrofluorination eventually occurs, but at significantly higher temperatures. 

The focus of more recent work has been the use of relatively low concentrations of additives in other oil recovery processes. Of particular interest is the use of surfactants (qv) as CO2 (4) and steam mobiUty control agents (foam). Combinations of older EOR processes such as surfactant-enhanced alkaline flooding and alkaline—surfactant—polymer flooding show promise of improved cost effectiveness. 

The polymer is exposed to an extensive heat history in this process. Early work on transesterification technology was troubled by thermal—oxidative limitations of the polymer, especially in the presence of the catalyst. More recent work on catalyst systems, more reactive carbonates, and modified processes have improved the process to the point where color and decomposition can be suppressed. One of the key requirements for the transesterification process is the use of clean starting materials. Methods for purification of both BPA and diphenyl carbonate have been developed. 

In more recent work, several groups have reported on fermentative approaches to nicotinic acids from 3-picoIine. Jiodococcus (8), Jicinetobactorr (9), and Pseudomonas (10) have found utihty ia this appHcation. 

As computing capabiUty has improved, the need for automated methods of determining connectivity indexes, as well as group compositions and other stmctural parameters, for existing databases of chemical species has increased in importance. New naming techniques, such as SMILES, have been proposed which can be easily translated to these indexes and parameters by computer algorithms. Discussions of the more recent work in this area are available (281,282). SMILES has been used to input Contaminant stmctures into an expert system for aquatic toxicity prediction by generating LSER parameter values (243,258). 

The role of IR spectroscopy in the early penicillin structure studies has been described (B-49MI51103) and the results of more recent work have been summarized (B-72MI51101). The most noteworthy aspect of a penicillin IR spectrum is the stretching frequency of the /3-lactam carbonyl, which comes at approximately 1780 cm" This is in contrast to a linear tertiary amide which absorbs at approximately 1650 cm and a /3-lactam which is not fused to another ring (e.g. benzyldethiopenicillin), which absorbs at approximately 1740 cm (the exact absorption frequency will, of course, depend upon the specific compound and technique of spectrum determination). The /3-lactam carbonyl absorptions of penicillin sulfoxides and sulfones occur at approximately 1805 and 1810 cm respectively. The high absorption frequency of the penicillin /3-lactam carbonyl is interpreted in terms of the increased double bond character of that bond as a consequence of decreased amide resonance, as discussed in the X-ray crystallographic section. Other aspects of the penicillin IR spectrum, e.g. the side chain amide absorptions at approximately 1680 and 1510 cm and the carboxylate absorption at approximately 1610 cm are as expected. 

In more recent work, Lockhart and Thompson have formed derivatives of 3 by substituting the secondary nitrogen. Substituents include CO—CH2—CH2—CH2—COOH and CH2CH2CH2 0Et. The latter compound should exhibit quite interesting binding properties for alkali metals, but binding constants for these compounds do not appear to have been determined. 

There are two common choices for the error vector it can either be a geometry or a gradient vector, the latter being preferred in more recent work. ... 

General accounts of prototropic tautomerism have been presented by Ingold and Baker" these include an outline of the historical development of the subject in which heteroaromatic compounds are discussed incidentally, and, therefore, such a historical account will not be given here. Of historical interest are Eistert s book on tautomerism and mesomerism which was published in 1938, a review on — NH-CO— tautomerism by Arndt and Eistert published in 1938, and Heller s account of heterocyclic tautomerism which appeared in 1925. Although more recent works on heterocyclic chemistry (e.g., references 9-11) have dealt incidentally with tautomerism, no unified... 

Hine and co-workers have since shown this scheme to be general for a variety of fluorine-free haloforms, and more recent work by Robinson has led to an improved rate expression for the basic hydrolysis of... 

More recent work has shown that the 2-unsubstituted compound 40 (R = H, R = Pr ) is an effective formyl anion equivalent which reacts at C2 and undergoes both 1,4-addition to a,(3-unsaturated carbonyl compounds and 1,2-addition to aldehydes (93TL3907 96T4719). 

More recent work from Attanasi et al. describes the preparation of pyrrole-pyrazol-3-one derivatives 136f-h by the sequential utihzation of conjugated azoalkene species that ended by heteroring closure. In summary, diazenyl esters... 

Trinitrochlorobenzene (76) treated with 1,3-propanedithiole and one equivalent of a base provided compound 479 and its treatment with additional base was reported to provide only small yields of benzodithiepine 480 (74CC672). A more recent work described that good yield (80%) of 480 was obtained by a treatment of 479 with triethylamine in benzene (76ZOR844). Similar treatment of 81 provided first spiro complex 481, which refluxed in acetone in the presence of triethylamine gave good yield of the denitrocyclization product 482 (Scheme 77) (92ZOR1496). 

In a more recent work the same research group has applied cyclic and acyclic vinyl ethers in the oxazaborolidinone-catalyzed 1,3-dipolar cycloaddition reaction with nitrones [30]. The reaction between nitrone 5 and 2,3-dihydrofuran 6 with 20 mol% of the phenyl glycine-derived catalyst 3c, gave the product 7 in 56% yield as the sole diastereomer, however, with a low ee of 38% (Scheme 6.9). 

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