Deuterated water production

Studies in deuterated water have shown that the hydroxyl proton does not end up in the ethanal formed. The decomposition of the 2-hydroxyethyl is not a simple P-elimination to palladium hydride and vinyl alcohol, which then isomerises to ethanal. Instead, the four protons stemming from ethene are all present in the initial ethanal product [6] (measured at 5 °C in order to suppress deuterium/hydrogen exchange in the product) and most authors have therefore accepted an intramolecular hydride shift as the key-step of the mechanism (see Figure 15.2). There remains some doubt as to how the hydride shift takes place. 

Isotope effects can be used to choose the most likely path. When ethylene is oxidized in deuterated water, the acetaldehyde contains no deuterium hence, all four hydrogens in the acetaldehyde must come from the ethylene. Thus, if the slow step of the reaction involves the formation of acetaldehyde, the activated complex for this slow step would involve a hydride transfer, and a primary isotope effect would be expected when deuterated ethylene is used. Actually, the isotope effect kn/ko was found to be only 1.07. In Paths 1 and 3, the slow step is, respectively, the decomposition of a 7r-complex and a a-complex to product, and they would be expected to display a primary isotope effect. However, in Path 2, the rate-determining step is the rearrangement of a 7r-complex to a (T-complex. Since no carbon-hydrogen bonds are broken, no primary isotope effect would be expected. Thus, Path 2 is consistent with all the experimental facts. Paths involving oxypalladation adducts, first suggested by the Russian workers (32), are now generally accepted (19, 28, 32). 

To confirm the tentative assignments of the degradation products and to further elucidate the structures of Deg-4, Deg-5, and Deg-6, HPLC/NMR analyses were performed. Conditions were as described for HPLC/UV and MS, with the exception that NMR-grade acetonitrile and deuterated water were used as mobile-phase components. The injection volume was additionally increased to 25 ml to place 5-50 pig of each degradation product on column. 

The behaviour of methyldiazonium ion in water has been investigated in phosphate buffer solutions at a pH of 7.4. The observations indicate that the methyldiazonium ion exchanges protons with deuterated buffers via an equilibrium involving diazomethane (equation 50). The products were recovered as deuterated methanol when the various labelled diazonium ions decomposed to the methyl carbocation, which reacted with deuterated water to form labelled methanol (equation 51). 

There is no equilibrium between 2 and 3 under the reaction conditions employed. However, the generation of palladium hydride (H-Pd) from adventitious water and syn addition of H-Pd to the alkyne portion is highly likely to initiate the six-membered ring carbocyclization. Thus, cyclizations in the presence of an excess amount (600 mol%) of deuterated water (D2O) were examined [51,52]. Indeed, the products D-2a and D-3a, which were regiospecif-ically deuterated at the exo olefin in the a position to the ester functionality, were obtained with -75% deuterium content (Scheme 8). 

The isotope effect, which q>pears when AH is replaced by AD and H in the reactant is replaced by D, plays an important role in studying acid-catalytic reactions. In particular, deuterated water dissociates to ions to a less extent than H2O the ratio of ion products = 7.47 and A A = 16.4 (298 K). For oxy acids in H2O... 

Fig. 29. SIMS profiles of total deuterium density in two composite samples subjected to a one hour deuteration in the same plasma product environment at 300°C (Johnson, 1988). Both samples had a substrate containing 2 x 10IH Sb/cm3 this was covered with an epitaxial layer containing 3 x 1018 As/cm3 for the upper curve, and with one containing 5x 10 7 As/cm3 for the lower curve. There was in both cases a little interdiffusion. All sample surfaces were prepared for deuteration by removing the oxide with a dilute HF etch, rinsing with distilled water, and blowing dry with heated nitrogen.

The conclusions on the rate limiting step are again supported by the differences in product selectivity if completely deuterated methanol is used the selectivity to dimethylether relative to formaldehyde is much larger. This is shown for the three catalysts in Figures 10-12, in which the ratio of the amounts of dimethylether and formaldehyde formed is plotted as a function of temperature. In the case of CH,0D, the water observed is a mixture of H20, HDO, and D20, most of it being HDO. 

A rapid technique for the identification of surfactants in consumer products by ESI-MS was proposed by Ogura and co-workers [6], After a simple preparation procedure, infusion of the sample, which was prepared in a water/methanol mixture (50 50) containing 10 mM ammonium acetate, allowed assignment of the [M + NH4]+ ions of Cio- and Ci2-mono- and -diglucoside in the mass spectrum (ion masses as in Table 2.7.1). The approach even permitted quantitative analysis when deuterated internal standards were used. 

The determination of alkyltrimethyl ammonium compounds with the general formula RN (CH3)3X surfactant were performed using CF-FAB and ESI. The compounds examined were dodecyl-, tetradecyl-, and hexadecyl-trimethyl ammonium compounds dissolved in water. The product ion spectra of dodecyltrimethyl ammonium compound and its methyl-deuterated homologue were presented. The product ion at m/z 60 [(CH3)3NH]+of the non-deuterated compound at m/z 228 was the only ion that shifted after deuteration to m/z 69 [38],... 

Deuterium may be analyzed from density measurements of waters. A confirmation method recommended here is GC mass spectrometry. Deuterium is burned in oxygen (or air) to form D2O which may be separated with helium on a GC column (of intermediate polarity) and identified from its mass spectra. The mass to charge ratio of the molecular ion is 20. Additionally, deuterated products obtained by exchange reactions with hydrogen containing substances (other than those containing C—H bonds) may be separated on a capillary GC column and identified by mass spectrometry. 

Evidence for this mechanism is (1) two equivalents of RLi are required (2) the hydrogen in the product comes from the water and not from the adjacent carbon, as shown by deuterium labeling 209 and (3) the intermediates 31-33 have been trapped.210 This reaction, when performed in tetramethylenediamine, can be a synthetically useful method211 of generating vinylic lithium compounds (33), which can be trapped by various electrophiles such as D20 (to give deuterated alkenes), C02 (to give a, 3-unsaturated carboxylic acids—6-34), or DMF (to give a, 3-unsaturated aldehydes—0-105). 

One of the best procedures for the synthesis of 1,3-diphenylbenzo[c]furan (138) consists of the reaction of 3-phenylphthalide (102) with phenylmagne-sium bromide, 2- especially when the reaction mixture is worked up in the presence of hydroquinone. The primary product can be isolated as colorless crystals with mp 145°C (decomposition above 100°C) in the presence of acid this unstable compound loses water very rapidly. The stereochemistry of the hydroxyphthalan is not known with certainty presumably the cis isomer (137a) is formed first. In deuterated acetone equilibrium with the trans isomer (137b) is established. ° For the synthesis of 1,3-diphenylbenzo [cjfuran, the hydroxyphthalan need not be isolated. 

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