Neat water

Goh M C, Hicks J M, Kemnitz K, Pinto G R, Bhattacharyya K, Heinz T F and Eisenthal K B 1988 Absolute orientation of water-molecules at the neat water-surface J. Phys. Chem. 92 5074-5... 

By utilizing a solid support-based tetradentate A-heterocyclic carbene-palladium catalyst, cross couplings of aryl bromides with phenylboronic acid were achieved in neat water under air.121 A high ratio of substrate to catalyst was also realized. 

Figure 2. (a) Excess enthalphies of n-butoxyethanol/water at 55.0 °C from four replicate titrations, starting at neat water (b) continuations of the titrations of (a). 

As discussed earlier, vibrational spectroscopy in neat water is much more complicated, due to the effects of both intramolecular and intermolecular coupling between OH stretch chromophores. 

It is more difficult to perform ultrafast spectroscopy on neat H20 (than it is on H0D/D20 or HOD/H20) since the neat fluid is so absorptive in the OH stretch region. One innovative and very informative technique, developed by Dlott, involves IR pumping and Raman probing. This technique has a number of advantages over traditional IR pump-probe experiments The scattered light is Stokes-shifted, which is less attenuated by the sample, and one can simultaneously monitor the populations of all Raman-active vibrations of the system at the same time. These experimental have been brought to bear on the spectral diffusion problem in neat water [18, 19, 75 77],... 

Photon echo and IR pump-probe experiments can also be performed on neat water, but one needs a very small sample. Fabrication of nano-fluidic Si3Ni4 sample cells have opened up this new and exciting field, and data from these experiments, performed by the Elsaesser and Miller groups, have recently been reported [73, 74]. At room temperature, spectral evolution occurs within 50 fs, and polarization anisotropy decays within 75 fs. At temperatures just about the freezing point, spectral evolution slows down dramatically [74],... 

Theoretical calculations for ultrafast neat water spectroscopy are difficult to perform and difficult to interpret (because of the near-resonant OH stretch coupling). One classical calculation of the 2DIR spectrum even preceded the experiments [163] Torii has calculated the anisotropy decay [97], finding reasonable agreement with the experimental time scale. Mixed quantum/ classical calculations of nonlinear spectroscopy for many coupled chromo-phores is a daunting task. We developed the TAA for linear spectroscopy, and Jansen has very recently extended it to nonlinear spectroscopy [164]. We hope that this will allow for mixed quantum/classical calculations of the 2DIR spectrum for neat water and that this will provide the context for a molecular-level interpretation of these complex but fascinating experiments. 

A modified rare earth catalyst (30) which is based on a polystyrene backbone as depicted in Scheme 4.15 can be applied even in neat water. It is attached via a hydrophobic oligomeric linker which creates a nonpolar reaction environment and acts as a surfactant for the substrates. The reaction of 4-phenyl-2-butanone with tetraallyltin in water using 1.6 mol% of the scandium catalyst (30) afforded the corresponding homoallylalcohol in a yield of 95%. Interestingly, when using other solvents (dichloromethane, acetonitrile, benzene, ethanol, DMF) the yields decreased drastically, indicating a much higher reaction rate in water [98]. 

In accordance with the suggested mechanism aryl iodides react easily (Scheme 6.2). At 80-100 °C, iodobenzene and acrylic acid gave cinnamic acid in neat water with [Pd(OAc)2] as catalyst and a mix of NaHCOs and K2CO3 as base [12]. Similar reactions were mn in water/acetonitrile 1/1 with... 

The reaction is catalyzed by palladium complexes either pre-formed, as [Pd(TPPMS)3] [13], or prepared in situ from (usually) [Pd(OAc)2] and various phosphines [21,23-27], TPPTS being one of the most frequently used [14]. Other precursors, e.g. [ PdCl(T -C3H5) 2] and so-caUed ligandless (phosphine-free) Pd-catalysts can also be effective. In fact, in several cases a phosphine inhibition was observed [23]. The solvent can be only slightly aqueous (5 % water in CH3CN, [14]) or neat water [26]. In the latter case a biphasic reaction mixture (e.g. with toluene) facilitates catalyst separation albeit on the expense of the reaction rate. A short selection of the reactions studied in aqueous solvents is shown on Scheme 6.9. 

Similar to the case of Suzuki couplings (6.1.2), ally lie alkylations can also be run in neat water as solvent in the presence of surfactants. In addition to the general solubihzation effect, the amphiphiles may also have a specific influence on the reaction rate. For example, the reaction of the P-ketoester substrate on Scheme 6.22 with allyl acetate, catalyzed by [Pd(PPh3)4] was only slightly accelerated by the anionic SDS (1.5 h, 18 % yield), however, the reaction rate dramatically increased in the presence of the cationic CTAB and the neutral Triton X-100 detergents, leading to 74 % and 92% yields in 1.5 h and 5 min ( ), respectively [51]. Several other carbonucleophiles were alkylated in such emulsions with excellent yields. 

The alcoholysis rate decreases by either increasing the steric bulk of the alcohol or decreasing its nucleophUicity (i.e., MeOH > EtOH > PrOH > BuOH 2,2,2-tri-fluoroethanol). Parallel to the decrease of the chain-transfer rate, the molecular weight of the copolymer increases. An effective role of water as hydrolysis agent in alcoholic media appears very unlikely as HOOC-terminated polyketone or oligo-ketone have never been observed. Obviously, in neat water, hydrolysis is a feasible chain-transfer path, leading to acid-terminated materials [13]. 

Most HPLC equipment currently available has a high tolerance to most mobile-phase conditions that can be contemplated for use in RPC applications with peptides. If it is intended to use mobile phases containing halide salts in RPC separations of peptides with standard HPLC equipment made from type 316 stainless steel, it is essential that the equipment is properly flushed with neat water when not in operation to avoid corrosion by the residual halide ions, especially at low pH. Otherwise, the use of the less popular biocompatible metal-free HPLC equipment, marketed by several manufacturers, avoids potential problems of equipment malfunction due to corrosion of the stainless steel or the contamination of peptide samples by low levels of leached metal ions. With such metal-free HPLC equipment, titanium, glass, or perfluoro-polymeric components have been used to replace any wettable stainless steel components. 

Figure 8 The time-dependent behavior of the hydrated electron obtained in the subpicosecond pulse radiolysis of neat water using 2-mm optical path sample cell, monitored at the wavelength of 780 nm.

Wan and Davis135,138 modified rhodium complexes with the water soluble chiral tetrasulfonated binap ligand 26 (Table 2) and used them as catalysts in the asymmetric hydrogenation of 2-acetamidoacrylic acid in aqueous media. The e.e. observed in neat water using Rh/26 was approximately the same as that obtained with the unsulfonated Rh/binap in ethanol (68-70% versus 67%).135... 

Assel A, Laenen R, Laubereau A (2000) Femtosecond solvation dynamics of solvated electrons in neat water. Chem Phys Lett 317 13-22... 

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