Acetone ionization

Question. For X-ray photoelectron spectra of a mixture of acetone and carbon dioxide gases, explain what you would expect to observe regarding the relative ionization energies (binding energies) and intensities in the C Is and O Is spectra. 

Various types of detector tubes have been devised. The NIOSH standard number S-311 employs a tube filled with 420—840 p.m (20/40 mesh) activated charcoal. A known volume of air is passed through the tube by either a handheld or vacuum pump. Carbon disulfide is used as the desorbing solvent and the solution is then analyzed by gc using a flame-ionization detector (88). Other adsorbents such as siUca gel and desorbents such as acetone have been employed. Passive (diffuse samplers) have also been developed. Passive samplers are useful for determining the time-weighted average (TWA) concentration of benzene vapor (89). Passive dosimeters allow permeation or diffusion-controlled mass transport across a membrane or adsorbent bed, ie, activated charcoal. The activated charcoal is removed, extracted with solvent, and analyzed by gc. Passive dosimeters with instant readout capabiUty have also been devised (85). 

Steiic effects of another kind become important in highly branched substrates, in which ionization is facilitated by relief of steric crowding in going from the tetrahedral groimd state to the transition state for ionization. The ratio of the hydrolysis rates in 8OV0 aqueous acetone of t-butyl /F-nitrobenzoate and 2,3,3-trimethyl-2-butyl p-nitrobenzoate is 1 4.4. 

A bell-shaped pH-rate profile can also be produced in a two-step reaction involving a single ionizable group if the rate-determining step changes when the pH is altered. An example, the oximation of acetone, is shown in Fig. 5-12. 

Reactions that occur with the development of an electron deficiency, such as aromatic electrophilic substitutions, are best correlated by substituent constants based on a more appropriate defining reaction than the ionization of benzoic acids. Brown and Okamoto adopted the rates of solvolysis of substituted phenyldimeth-ylcarbinyl chlorides (r-cumyl chlorides) in 90% aqueous acetone at 25°C to define electrophilic substituent constants symbolized o-. Their procedure was to establish a conventional Hammett plot of log (.k/k°) against (t for 16 /wcra-substituted r-cumyl chlorides, because meta substituents cannot undergo significant direct resonance interaction with the reaction site. The resulting p value of —4.54 was then used in a modified Hammett equation. 

For purification the crude quaternary salt was dissolved in hot ethyl alcohol (2 ml/g) and warm dry acetone (8 ml/g) was stirred into the clear filtrate. On cooling, 387 g (78% recovery) of a pure white powder, MP 195°Cto 197°C, were obtained, in which the ionizable chlorine assayed at 99.7% of the theoretical value. 

DNA sequencing and. 1113 Electrospray ionization (ESI) mass spectrometry, 417-418 Electrostatic potential map, 37 acetaldehyde, 688 acetamide, 791,922 acetate ion. 43. 53, 56, 757 acetic acid. 53. 55 acetic acid dimer, 755 acetic anhydride, 791 acetone, 55, 56. 78 acetone anion, 56 acetyl azide, 830 acetyl chloride, 791 acetylene. 262 acetylide anion, 271 acid anhydride, 791 acid chloride, 791 acyl cation, 558 adenine, 1104 alanine, 1017 alanine zwitterion, 1017 alcohol. 75 alkene, 74, 147 alkyl halide, 75 alkyne. 74... 

Values were selected from the 47 entries given in Ref. 19. The rate constants were determined in acetone-water at 25.0 °C. and the ionization constants in water at 25.0 °C. 

Among the experiments that have been cited for the viewpoint that borderline behavior results from simultaneous SnI and Sn2 mechanisms is the behavior of 4-methoxybenzyl chloride in 70% aqueous acetone. In this solvent, hydrolysis (i.e., conversion to 4-methoxybenzyl alcohol) occurs by an SnI mechanism. When azide ions are added, the alcohol is still a product, but now 4-methoxybenzyl azide is another product. Addition of azide ions increases the rate of ionization (by the salt effect) but decreases the rate of hydrolysis. If more carbocations are produced but fewer go to the alcohol, then some azide must he formed by reaction with carbocations—an SnI process. However, the rate of ionization is always less than the total rate of reaction, so some azide must also form by an Sn2 mechanism. Thus, the conclusion is that SnI and Sn2 mechanisms operate simultaneously. ... 

The primary method for detecting methyl parathion and metabolites in biological tissues is gas chromatography (GC) coupled with electron capture (BCD), flame photometric (FPD), or flame ionization detection (FID). Sample preparation for methyl parathion analysis routinely involves extraction with an organic solvent (e g., acetone or benzene), centrifugation, concentration, and re suspension in a suitable solvent prior to GC analysis. For low concentrations of methyl parathion, further cleanup procedures, such as column chromatography on silica gel or Florisil are required. 

The rate of solvolysis of the phosphinic chlorides (83a, b) in trifluoro-acetic acid and aqueous acetone (the composition of the latter solvent being chosen such that the rate of S nI solvolysis of Bu Cl was the same in both) have been examined to assess the possible operation of an 5 n1(P) ionization mechanism. In the more nucleophilic aqueous acetone solvent,... 

Figure 7a demonstrates that FTMS can simultaneously detect ions over a broad mass range. This is the actual high resolution mass spectrum, not a stick plot. This spectrum was obtained when a mixture of CO,, C H., and acetone was leaked into the chamber and ionized by the electron beam. The total sample pressure was... 

Roussis SG, JW Fedora (1997) Determination of alkenes in hydrocarbon matrices by acetone chemical ionization mass spectrometry. Anal Chem 69 1550-1556. 

The products were identified by comparing the retention times of the reaction products with commercial compounds, and by GC-MS analysis in a Hewlett-Packard 5973/6890 GC equipped with an electron impact ionization at 70 eV detector and a cross-linked 5% PH ME siloxane (0.25 mm coating) capillary column. The reaction products were separated from the catalyst with filter syringes and analyzed in an Agilent 4890D and a Varian 3400 GC equipped with a flame ionization detector, and CP-Sil 8CB (30 m x 0.53 mm x 1.5 pm) and DB-1 (50 m x 0.52 mm x 1.2 pm) columns, respectively. Decane was used as an internal standard. The catalyst was thoroughly washed after reaction with acetonitrile, acetone and water, and dried overnight under vacuum at 40°C. 

If the solvent is not protogenic but protophilic (acetone, dioxan, tetrahydrofuran, dimethylformamide, etc.), self-ionization obviously does not occur. Consequently, the dissolved acids are dissociated to a greater or lesser degree but dissolved bases do not undergo protolysis. Thus, there can exist only strong acids but no strong bases in these solvents. The pH is not defined for a solution that does not contain a dissolved acid (i.e. in the pure solvent or in the solution of a base). The pKA value can be defined but not... 

Figure 14. Reflectron-TOF spectra of acetone (T) cluster ions. Am (T)mH+, Bm (T)mCH5, Cm = (T)mC2H30+. (a) 0.4% water in the acetone sample, (T)i C6HnO+ (mass 157) and (T)2-C6HnO+ (mass 215) are seen, whereas ion signal corresponds to (T)3-H30+ (mass 193 is not found), (b) 0.7% water in the acetone sample, all peaks corresponding to masses 157, 215, and 193 are observed, (c) 1.0% water in the acetone sample, ion peaks corresponding to (T)vC6HnO+ (mass 157) and (T)2 C6HnO+ (mass 215) are not seen however, (T)3-H30+ (mass 193) is clearly identified. Neutral clusters are ionized at 355 nm using a pulsed Nd YAG laser. Taken with permission from ref. 2.

Toullec, 1982). The values of log/C in water at 25°C have been estimated for acetone as —7.02 and acetophenone as —6.63 (Guthrie, 1979). However, the pKa-values of the ketones ionizing from the ketone to the enolate according to (4) have been measured, using either an acidity function method... 

The source of some of the difficulties encountered in trying to explain the effects of structural changes on ionization rates may be due to the different parts played by the solvent, as for example, the sulfur dioxide of the trityl chloride equilibrium experiments and the aqueous acetone of the benzhydryl chloride rate data. The solvent is bound to modify the effect of a substituent, and although the solvent is usually ignored in discussing substituent effects this is because of a scarcity of usable data and not because the importance of the solvent is not realized "... solvation energy and entropy are the most characteristic determinants of reactions in solution, and... for this class of reactions no norm exists which does not take primary account of solvation. 220 Precisely how best to take account of solvation is an unanswered problem that is the subject of much current research. 

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