Carbonate quats

Dimethylcarbonate (DMC) has found some use as an alkylating agent to produce either methocarbonate quats or bicarbonate quats (after hydrolysis). DMC is a fairly weak alkylating agent and reactions are often run at elevated temperatures with an excess of DMC and methanol as a solvent/catalyst. Other carbonates can be used to make bicarbonate and carbonate quats by an in situ transesterification-quaternization process [35]. The attraction of dimethyl carbonate is that it has a good environmental profile and the quats produced do not have the corrosivity shown by chloride quats, making them favoured for wood preservation where corrosion of nails, screws and staples is a concern. 

PT catalysts are often difficult to separate from the product, while it is also desirable that the catalyst should be reusable or recyclable. Distillation and extraction are the most common separation processes. The main disadvantage of lipophilic quats is their tendency to remain in the organic phase and consequently contaminate the product. Therefore, extraction in water often is not satisfactory. Furthermore, products in the fine chemicals industry often have high boiling points and/or are heat sensitive, which makes separation of the catalyst by distillation impossible. Often the only means to remove the catalyst in these cases is to adsorb it using a high surface area sorbent such as silica, Florisil or active carbon (Sasson, 1997). After filtration, the catalyst can then be recovered by elution. 

Kong J, Soh HT, Cassell AM, Quate CF, Dai HJ. 1998. Synthesis of individual single-walled carbon nanotubes on patterned silicon wafers. Nature 395 878-881. 

Smith PE, Farquhar RM Hancock RG (1991) Direct radiometric age determination of carbonate diagenesis using U-Pb in secondary calcite. Earth Planet Sci Lett 105 474-491 Spalding RF, Mathews TD (1972) Submerged stalagmites from caves in the Bahamas Indicators of low sea level stand. Quat Res 2 470-472... 

Nitrite substitutes can be divided into seven chemical categories (1) amine benzoates (2) fatty acid amines (3) phosphate or carbonate silicates (4) organophosphates (5) amine borates (6) alkanolamines and (7) quaternary ammonium compounds ("quats"). Thus, the technology already exists for replacing nitrite with no loss in rust protection. However, most replacements for nitrite are more expensive, less effective, less likely to be compatible with other additives, and work by a different mechanism (12). It is therefore not surprising that fluids containing nitrite are still relatively com mon. 

The general feature of alkylation reactions at a carbon atom is that they can be achieved under sonication using solid bases even in apolar solvents. The advantage is that side reactions are generally minimised. Deprotonation occurs readily on a benzylic position in the presence of aqueous sodium hydroxide, as shown with indene (Eq. 3.21) [117]. A quantitative yield of the alkylated product can be obtained using sonication in the presence of a PTC. It was suggested that alkylation of cyclopentadiene or indene by secondary or tertiary alkyl halides in the presence of potassium hydroxide and Ali-quat occurred via a SET process [118]. 

For these two fluids the attenuations do not follow a simple /2 law, and the values given correspond to measurements at 3 GHz for carbon disulphide and at 1 GHz for helium at 0.4 K and at 0.1 K. The data in this table were taken from Lemons and Quate (1979), Kaye and Laby (1986), Selfridge (1985), Wickramasinghe and Petts (1980), Heiserman etal. (1980), and Foster and Rugar (1985). 

Carbon-Oxygen and Carbon-Sulfur Bonds. A report of modest enantioselectivity up to 48% ee in the 0-alkylation of racemic secondary alcohols (a kinetic resolution) in the presence of a chiral non-racemic non-functionalized quat, (S)-Et3NCH2CH(Me)Et Br, could not be repeated [80]. Such catalysts would not be capable of making the multipoint interaction between catalyst and reactants in the transition state, which are thought to govern the stereochemistry of these types of reactions. Other O-alkylations are noted [lie]. 

Carbon-Halogen Bond. Early chlorination of various alkenes gave only low rotations in the isolated products with either ephedra or cinchona quats [33b]. 

QUATE multiplet corresponding to signal 4 in the 13C spectrum of 2-chlorobutane. Because the two one-bond coupling constants are nearly equal (ca. 35 Hz between tetrahedral carbons Section 9.3), the two doublets are barely resolved, appearing instead as one doublet at lower resolution. 

Along with the DEPT pulse sequence, a useful complement is the QUAT sequence, which detects only quaternary carbons (S4)- As illustrated in Figure... 

QUAT experiment is that long recovery times are necessary for optimum acquisition of the slowly relaxing quaternary carbons. 

McKay, J. L., Pedersen, T. F., andKienast, S. S. (2004). Organic carbon accumulation over the last 16 kyr off Vancouver Island, Canada Evidence for increased marine productivity during the deglacial. Quat. Sci. Rev. 23(3-4), 261-281. 

Wang H., Liu C. L., and Follmer L. R. (1998) Climatic trend and habitat variation based on oxygen and carbon isotopes in paleosols from Liujiapo, Shaanxi, China. Quat. Int. 51/52, 52-54. 

Curry W. B. and Lohmann G. P. (1982) Carbon isotopic changes in benthic foraminifera from the western South Atlantic reconstructions of glacial abyssal circulation patterns. Quat. Res. 18, 218-235. 

Duplessy J.-C., Shackleton N. J., Matthews R. K., Prell W., Ruddiman W. F., Caralp M., and Hendy C. H. (1984) C record of benthic foraminifera in the last interglacial ocean implications for the carbon cycle and the global deep water circulation. Quat. Res. 21, 225-243. 

Alexandre A., et al. (1999) Late Holocene phytolith and carbon-isotope record from a latosol at Salitre, south-central Brazil. Quat. Res. 51(2), 187-194. 

Fredlund G. G. and Tieszen L. L. (1997b) Phytolith and carbon isotope evidence for Late Quaternary vegetation and climate change in the southern Black Hills, South Dakota. Quat. Res. 47(2), 206-217. 

Jahren A. H., et al. (2001) Paleoclimatic reconstruction using the correlation in 8 0 of hackberry carbonate and environmental water. North America. Quat Res. 56(2), 252-263. 

Wang Y., Jahren A. H., and Amundson R. (1997) Potential for C dating of biogenic carbonate in hackberry Celtis) endocarps. Quat. Res. 47, 337-343. 

Figure 6 The Holocene ice-core record of the variability of methane, carbon dioxide, and S C02- (a) The methane record from ice cores in Greenland and Antarctica, showing significant variability including variability in the interpolar gradient (Chappellaz et al., 1997). (b) The results of a three-box model used to infer the latitudinal distribution sources of methane at four different time spans during the Holocene Epoch (Chappellaz et al., 1997). (c, d) The carbon dioxide concentration and its isotopic composition from Taylor Dome, Antarctica (Indermuhle et al., 1999). Note the dissimilarities among the trends in this figure (Raynaud et al. (2000) reproduced by permission of Elsevier from Quat. Set. Rev., 2000, 19, 9-17 (figure 1)).

Maslin M. A. and Thomas E. (2003) Balancing the deglacial global carbon budget the hydrate factor. Quat Sci. Rev. 22, 1729-1736. 

Sundquist E. T. (1991) Steady- and non-steady-state carbonate-silicate controls on atmospheric CO2. Quat. Sci. Rev. 10,... 

Denniston, R.F., Gonzalez, L.A., Asmerom, Y., Reagan, M.K. and Recelli-Snyder, H., 2000b, Speleothem carbon isotopic records of Holocene environments in the Ozark Highlands, USA, Quat. Internatl. 67 21-27. 

Reactions.—Nucleophilic Attack at Carbon. A number of studies of the kinetics of quaternization of phosphines have been reported, all of which lend support to an earlier suggestion that the transition state for such reactions is reactant-like. From the rates of quaternization of a series of heteroaryldiphenylphosphines (54) with a-bromoacetophenone, it was concluded that the r-excessive heterocyclic substituents are not significantly involved in pj,-d conjugative stabilization of the developing phosphonium centre in the transition state of the reaction. Similarly, there is little evidence of conjugative effects in the transition state for quat nization of... 

Analysis of distortion enhancement by polarization transfer (DEPT) C-NMR and quaternary-C only (QUAT) subspectra of a soil HA and a soil FA suggest that carboxylate groups, of which the FA is richer than the HA, play a prominent role in the binding of Eu " " to HS (Shin et al., 1996). This result is consistent with the higher binding constant measured for Eu " " with FA than with HA, which is richer than FA in aromatic carbon and aliphatic methine and quaternary carbons. 

Cerling, T.E. Hay, R.L, (1986) An isotopic study of paleosol carbonates from Olduvai Gorge. Quat. Res., 25, 63-78. 

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