Protonated solvent

The dissociation, or autoprotolysis constant for a solvent, SH, relates the concentration of the protonated solvent, SH2, to that of the deprotonated solvent, S . For amphoteric solvents, which can act as both proton donors and proton acceptors, the autoprotolysis reaction is... 

You should recognize that is just the specific form of Ks for water. The plT of a solution is now seen to be a general statement about the relative abundance of protonated solvent... 

Acids that are better proton donors than the solvent are leveled to the acid strength of the protonated solvent bases that are better proton acceptors than the solvent are leveled to the base strength of the deprotonated solvent. 

An example of proton (H ) transfer from a protonated solvent molecule (SH ) or cluster to form a quasi-molecular ion (MH ) of the substrate (M). 

GTP is a safe operation. A runaway polymerization can be quickly quenched with a protonic solvent. Since the group transfer polymerization goes to completion, no unwanted toxic monomer remains the silicone group on the living end after hydroxylation is removed as inactive siloxane. The living polymer in GTP is costlier than traditional polymerization techniques because of the stringent reaction conditions and requirements for pure and dry monomers and solvents. It can be used in fabrication of silicon chips, coating of optical fibers, etc. 

These four solvents can thus be termed protogenic solvents, whilst bromine trifluoride and sulphur dioxide which do not contain hydrogen are non-protonic solvents. Non-ionising solvents include hydrocarbons, ethers, esters and higher alcohols the lower alcohols, especially methanol and ethanol, do show slight ionising properties with appropriate solutes. 

For SOMe and S02Me the values of as determined through chemical reactivities in weakly protonic solvents are quoted as 0.52 and 0.60 respectively. These provide a point of reference for consideration of the values determined through 19F NMR studies. The values for these substituents as determined in normal solvents are given as +0.49 and... 

Evidence has been presented from F-nmr shielding effects in m- and p-substituted fluorobenzenes (10) that solvent interaction modifies the O/ values of a number of the substituents of Table V (specifically NMc2, NH2, NHCOMe, OMe, CH3SO, SF3, CF3SO, CF3, SO3ME, CN, CO2R, NO2 and MeCO). The indicated changes in Oj between hydrocarbon and weakly protonic solvents are... 

We normally avoid protonated solvents, because the very intense solvent peak will obscure nearby protons, and the dynamic range problem will also... 

It is known that lifetime of solvated peroxyde ion-radicals vary in different solvents. Thus, it amounts to hours in pyridine and dimethyl-sulphoxide but falls far short of a minute in proton solvents like water or alcohols [56, 57]. 

The above solvents theory (A) and proton theory (B) have shown that in theory the neutrality point (of the pure solvent) lies for the amphiprotic solvents at pH = pKs and for the aprotic protophilic solvents at a pH somewhere between the highest acidity (of the protonated solvent) and an infinitely high pH. However, the true pH of the neutrality point of the solvent can only be obtained from a reliable pH measurement and the problem is whether and how this can be achieved. For water as a solvent, the true pH = - logaH+ = colog aH+ is fixed by the internationally adopted convention E°m ( H2(latm) = 0... 

Synthesis and Spectroscopic Characterization. 3-(Methyldichlorosilyl)-pyridine (1) was synthesized by the reaction of 3-lithiopyridine, prepared in situ from 3-bromopyridine and n-butyllithium, with a large excess of methyltrichlorosilane at -76° (Scheme 2). The product is a colorless distillable liquid which is soluble in aromatic, aliphatic and chlorinated hydrocarbons and extremely sensitive to moisture and protonic solvents. 

It is normal in conventional NMR to work with deuterated solvents, which serve both for optimising magnetic field homogeneity (lock, shim) and for avoiding the presence of the unwanted strong signals from protonated solvents. 

Protonic solvents such as methanol or acetonitrile are commonly employed, often with the addition of formic or acetic acid or bases such as hexylamine, to aid gas phase ionisation. 

Of more intrinsic interest are processes involving two electrons, since these constitute the great bulk of organic reductive processes, especially in protonic solvents. The reason for this is that the first electron transfer will generate an unstable radical species, whereas the second can regenerate a stable closed-shell product. One example that we have already encountered is C02 reduction but a case that has been well studied is that of quinone reduction as ... 

Some ionizing solvents are of major importance in analytical chemistry whilst others are of peripheral interest. A useful subdivision is into protonic solvents such as water and the common acids, or non-protonic solvents... 

It will be seen from these examples that the process of self-ionization in a protonic solvent involves the transfer of a proton from one solvent molecule to another. Thus, the solvent is acting simultaneously as a Lowry-Bronsted acid and as a base. 

A final subdivision of ionizing protonic solvents can be made in terms of the behaviour of the solvent towards available protons from a solute. A basic or protophilic solvent such as ammonia or an amine will coordinate protons strongly, and in so doing accentuate the acidic properties of the acid. 

The Lowry-Bronsted concept provides a basis for the interpretation of reactions in protonic solvents. This concept may be summarized by considering the generalized equilibrium... 

Scheme 4-21 shows the preparation of L-threitol and L-erythritol.38 Epoxy alcohols (2J ,3iS)-61 and (2S,3/ )-61. generated by asymmetric epoxidation, are exposed to sodium benzenethiolate and sodium hydroxide in a protonic solvent to undergo base-catalyzed rearrangement, yielding the threo-diol 62 and erythro-diol 63, which can then be converted to the corresponding tetraacetate of l-threitol 67 and L-erythritol 69 through subsequent transformations. 

If your compound does not happen to dissolve in CC14, you still have a shot because deuterium atoms do not give PMR signals. This is logical, since they re not protons. The problem is that deuterated solvents are expensive, so do NOT ask for, say, D20 or CDC13, the deuterated analogs of water and chloroform, unless you re absolutely sure your compound will dissolve in them. Always use the protonic solvents — H20 or CHC13 here — for the solubility test. There are other deuterated solvents, and they may or may not be available for use. Check with your instructor. 

---