Any standard solvents may be obtained from the NMR operators. There are currently in stock:
Special solvents, lanthanide shift reagents (chiral, achiral), and special reagents like chiral solvents are available on request.
Here you can look up properties of deuterated solvents (1H-, 13C-chemical shifts, water signal chemical shift, melting-, boiling points, prices; in German). This table was kindly provided by Fritz Kastner, University of Regensburg.
The following is an outline by Prof. J. A. Gladysz about usage of diverse solvents with respect to special demands of the Gladysz group.
One of the painfully-learned lessons of research is "never to trust the purity of any starting material" or "assay everything". Since the NMR lab is used to sensitive RLi compounds, we are probably in very good hands. Most rhenium compounds are in fact not very water/O2 sensitive. However, many of our phosphines rapidly form phosphine oxides in solvent with O2 traces. There will be other projects with very sensitive species.
Some general recommendations are as follows:
|Toluene-d8||Very good for low temperature and high temperature work|
|Benzene-d6||We have a lot of data in this solvent, which is cheaper than
toluene-d8. However, it is not my favorite since
chemical shifts can be very different from chlorinated
A lot of carbon chain complexes have been measured in benzene.
|Chlorobenzene-d5||A very good solvent, not too expensive. It freezes at -45 degrees, limiting low temp work. However, it is high boiling. More polar than benzene/toluene, which is what you like.|
|C6D5CF3||This would be a valuable deuterated solvent, and Ralf Meier has researched the best method. We should have someone make it.|
|CDCl3||This solvent (USA purity) has a good record with us. It usually will dissolve cations.|
|CD2Cl2||This solvent is excellent. It doesn't freeze until -98 degrees, and is ideal for low temperature exploratory chemistry. We often use CH2Cl2 and just monitor by phosphorus. The -d2 solvent is much more expensive, but is a cost we have to swallow in our research.|
|CDFCl2||Another outstanding solvent that can be used down to -140 degrees.
It must be prepared, the reference is #18 in paper #143,
see Figure 1
for some typical data. You can detect all sorts
of isomers at such low temps; the prep is not too expensive.
***note: the above halogenated solvents CAN be used to monitor RLi/RMgX reactions; almost always the organometallic compound will react faster than the solvent****
|Acetone-d6||This is a fine solvent, not too expensive, although not as polar as others given below (something soluble in acetone is almost always soluble in a halogenated solvent)|
|CD3CN||This is usually the #1 choice when a more polar solvent is needed. If the solvent reaction with the metal complex, one usually gets a well defined (previously prepared) complex|
|DMSO-d6||This is usually a poor choice. Don't let a NMR technician use it by default. It is not expensive (hence popular), but if you look at nucleophilicity scales MeSMe and DMSO are among the most aggressive ligands for metals. And DMSO can give oxidation -or- substitution product. So when things go wrong, you get a big big mess.|
|CD3NO2||This is a reactive solvent, but I have had some good luck with it from time to time, for example with poorly soluble complexes. It is very polar.|
|THF-d8||This solvent hasn't been used very much in the group. The major reason is that rhenium cations aren't very soluble in ethers. It is also expensive. However, we have used it for following RLi additions, it has worked well.|
As a final comment: All expensive NMR solvents that do not become very contaminated by other NMR solvents can be recovered. In particular, prep GC allows 0.1 to 0.3 mL injections. One could set up one of the old prep GC's to do this job.
A. Water.Purging with inert gas or pumping on this
solvent will rid it of dissolved
oxygen. Dissolved salts may be removed by distillation or by utilizing a commercially
available deionizing system.
B. Saturated Hydrocarbons.
Purging and freeze-pump-thaw methods are
effective in degassing paraffins. Distillation with the elimination of the first
fractions produces dry solvent. Molecular sieves may also be used to remove
water. Distillation from sodium-benzophenone ketyl is highly effective in
obtaining very low levels of water and oxygen. Commercial grades of
hydrocarbons are often contaminated with olefins, which can be eliminated by
several washings with concentrated sulfuric acid, separation from the acid,
washing with water, and, after preliminary drying with
molecular sieves 4Å or 5Å,
subjecting the solvent to fresh desiccant or one of the drying procedures outlined
C. Aromatic Hydrocarbons.
The methods listed for saturated
hydrocarbons may be used with benzene. Thiophene and similar sulfur-containing
impurities are removed by sulfuric acid washes. Very-high-purity benzene may be
prepared by fractional crystallization from ethanol followed by distillation.
Toluene and xylenes are purified in the same manner as benzene; however, these
solvents should be kept cool (at or below room temperature) during sulfuric acid
treatment due to their greater reactivity toward sulfonation.
Molecular sieves provide a good means of drying these
materials. CAUTION: Strong reducing agents, such as metal hydrides, Na and
Na-K, react violently with halogenated hydrocarbons and should never be
used to dry these materials. Chloroform generally contains 1% ethanol to
suppress phosgene formation. This may be removed by shaking with concentrated
H2SO4, separating from the acid, washing with
water, predrying with molecular
sieves or silica gel, drying with molecular sieve 4Å,
and distilling, taking the
central fraction. This material must be used directly or stored
strictly out of contact
with the atmosphere. Methylene chloride is less reactive than chloroform and is not
prone to phosgene formation. It may be distilled from
P2O5 or dried with molecular
sieves and distilled under an inert atmosphere. (Note that traces of phosphine are
introduced into a material by the use of P2O5.)
Diethyl ether is available in very dry grades, which for most
purposes can be used directly from the freshly opened can. Similarly, purified
grades of tetrahydrofuran are available which are often sufficiently dry be used
directly (Fisher). When extremely sensitive materials are handled, diethyl ether
and tetrahydrofuran are often distilled from LiAlH. However, great care must be
taken first to remove all peroxides and never to let the still pot go dry.
Sodium-benzophenone ketyl is also effective with ethers which are
peroxide free, and it
has the advantage of being safer than LiAlH4. A small amount of benzene is
introduced into the solvent when sodium-benzophenone ketyl is used.
Acetonitrile is a convenient solvent for many ionic compounds, but
it is extremely difficult to dry to much better than millimolar in water.
degradation products of the solvent, ammonia and acetic acid, may be present.
Strongly acidic or basic drying agents react with this solvent and strong reducing
agents are ruled out. One recommended procedure is first to predry the solvent
with molecular sieves or silica gel if large quantities of water are present,1
stir or shake this material with calcium hydride, which will remove both
acetic acid and water. The predried acetonitrile is then distilled at a high reflux
ratio from P2O5 (less than 5 g/L) under an inert atmosphere.
A gel may form in the
distillation flask, and care should be taken to leave behind the bulk of the solvent
and residues in the distillation flask. The solvent is then refluxed over calcium
hydride and distilled under an inert atmosphere using a high reflux ratio and a
good fractionating column. The middle fraction is collected. Acrilonitrile is an
impurity which will contaminate the product if this distillation is not efficient.
As an alternative to this procedure, some workers advocate stirring acetonitrile with calcium hydride, distilling it under a dry inert atmosphere, and passing it through a highly activated alumina column under a dry inert atmosphere.
The removal of traces of water from methanol and ethanol is
difficult. Calcium turnings, magnesium turnings activated with iodine, and lump
calcium hydride are sometimes used to remove traces of water from methanol.
However, these active metals may contain some nitride and give rise to
contamination by ammonia. These same drying agents may be used with higher
alcohols. A column of dry molecular sieve 4Å is also effective in removing water
from ethanol and higher alcohols.
Acetone is very difficult to dry, since many of the usual drying
agents cause reaction, including MgSO4.
Storage over molecular sieve 4Å yields
relatively dry acetone. High-purity acetone may be obtained by saturating the
solvent with dry NaI at room temperature, decanting and cooling to -10oC,
isolating the crystals which form (NaI-acetone complex), warming the crystals to
room temperature, and distilling the resulting liquid.
1J. F. Coetzee, Pure and Appl. Chem., 13, 429-433 (1966).
For small amounts of deuterated THF, diethyl ether, benzene, and toluene, we found that sodium-lead alloy is a very convenient drying agent. Put an appropriate amount in a dry flask (ca. 20 ml) equipped with a teflon cock and rubber septa, evacuate and (preferably) heat under vacuum with a heat gun, flush with dry argon or nitrogen, then fill in the solvent (taken from an ampoule, preferably under argon) by means of a plastic syringe. Caution: THF may swell the syringe within a few minutes, so quick work is indicated. Water contents manifest in small hydrogen bubbles. Storing one or several days will remove residual water to an amount tolerable for virtually all purposes. Due to alloyed lead, the sodium surface is regenerated continuously. Sodium lead alloy may be safely destroyed by water (of course, hydrogen will evolve, so remove any fire sources).
Solvents from ampoules are strongly prefered over bottled solvents. I once achieved THF-d8 in a screw bottle, the water contents were extremely high, resulting in vigorous hydrogen evolution.
Prolongued exposure of a solvent to NMR rubber caps will swell the cap, eventually letting the solvent evaporate. Of course, the best choice is to seal an NMR tube for samples expected to be studied over longer periods. However, a very good though somewhat expensive alternative is to use NMR tubes equipped with screw caps (DM 40 per piece). These caps (teflon) provide a very good seal as long as they are not punctured. I have a sample of vinyllithium in THF-d8 in such a tube, prepared in 1991, which is still ok and is kind of a reference sample in our studies!
I confirm the above remarks by Shriver concerning acetone. Even small traces of acid or base will lead to reaction (self-condensation), leading to diacetone alcohol in the first step which manifests in 3 (at first strange) singlets in the 1H-NMR spectrum. In the presence of acid, water elimination follows leading to mesityl oxide.
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Institute of Organic Chemistry
Location: Rooms U34, U35, U36
University of Erlangen-Nürnberg
D-91054 Erlangen, Germany