The Purification of Common Organic Solvents
====================================
Commercially available grades of organic solvents are of adequate purity
for use in many reactions provided that the presence of small quantities
of water (the most widespread impurity in all organic solvents) is not
harmful to the course of the reaction, and also that the presence of other
impurities (e.g. ethanol in diethyl ether) is unlikely to cause undesirable
side reactions. The commercially available grades for general use are often
accompanied by specifications indicating the amount and nature of any
impurities present.
when however the levels of impurities , including moisture, are unacceptable
for particular reactions, and when large volumes of such solvents are likely to
be required, it is frequently more economic to purify the commercial grades
than to purchase the more expensive AnalaR grades. Solvents of the
appropriate grade of purity should also be used in isolation (extraction) and
purification (re-crystallization) processes, particularly in the latter stages
immediately prior to spectroscopic and/or elemental analysis.
Drying Solvents
====================
Rigorously dried organic solvents are frequently markedly hygroscopic.
The distillation assembly should therefore be protected by a suitable
drying tube. The redistilled material should be stored in a clean dry
bottle with a well fitting stopper which can, if necessary, be sealed
with paraffix wax. If exceptionally hygroscopic compounds need to be
stored, this is best done in sealed glass ampoules, but it is usually best
in such cases to use the material immediately after drying and purification .
It is often convenient to remove final traces of water with the aid of a
molecular sieve and to store the dried solvent in the presence of the sieve.
The descriptive term, molecular sieve, applies to a group of dehydrated
synthetic sodium and calcium aluminosilicate adsorbents (zeolites) which
have a crystal lattice structure incorporating uniformly sized holes or pores
which are able to accept molecules smaller than a limiting dimension; the
larger molecules do not diffuse into the lattice structure. This selectivity,
based upon molecular shape and dimension, accounts for the sieving
action and is particularly valuable for the removal from gases and liquids
of water, which readily diffuses into the pores and is retained by a strong
absorptive attraction. The pore size is determined by the nature of the
manufacturing process and currently five principal types are available in
bead, pellet or powder forms, namely Types 3A, 4A, 5A, 10X and 13X,
representing an effective pore diameter of approximately 0.3, 0.4, 0.5, 0.8 ,
and 1.0 nm respectively. All these are stable over a pH range 5--11 but
interaction with strong acids is to be avoided; grades are available which
are more resistant to the action of acid (e.g., AW-300, AW-500).
Types 3A, 4A, and 5A are those which are most usually employed for drying
purposes; 5A is also capable of adsorbing the higher homologues of
straight chain alkanes, alkenes and alcohols. The absorptive capacity for
water is higher than that of silica gel, alumina or activated charcoal. After use,
molecular sieves may be readily regenerated by heating between
150 and 300oC in a suitable oven or in a stream of dry air and
then cooling in a desiccator.
Solvents used for the preparation of solution for spectroscopic examination
(particularly infrared measurement) need to be rigorously purified or
spectroscopic grades must be purchased. It is advisable to dry the solvent
immediately before use by means of a molecular sieve.
https://en.wikipedia.org/wiki/Molecular_sieve
Saturated Aliphatic Hydrocarbons
======================================
1) Light petroleum :
The fractions of refined petroleum which are commonly used have
b.p. 40--60, 60--80, 80--100 and 100-120 oC. It is not
advisable to employ a fraction with a wider b.p. range than 20 oC,
because of possible loss of the more volatile portion during its use in
re-crystallization , etc., and consequent different solubility relationships
with the higher boiling residue . For some purposes the presence of
unsaturated (chiefly aromatic) hydrocarbons in light petroleum is
undesirable. Most of the unsaturated hydrocarbons may be removed
by shaking two or three times with 10 per cent of the volume of
concentrated sulphuric acid ; vigorous shaking is then continued with
successive portions of a concentrated solution of potassium
permanganate in 10 per cent sulphuric acid until the color of the
permanganate remains unchanged. The solvent is then thoroughly
washed with water, dried over anhydrous calcium chloride and distilled.
If required perfectly dry, it should be allowed to stand over sodium wire.
More recently a convenient method of purification has been recommended
which is to decant the solvent, previously treated with sulphuric acid,
directly on to a basic alumina (Grade I) column using about 50 g of
absorbent for each 100ml of solvent; the first 5 percent of eluate is
discarded. The column receiver should be suitably protected from the
ingress of moisture by the attachment of a calcium chloride tube.
Light petroleum fractions free from aromatic hydrocarbons are marketed,
as are the pure homologues, pentane, heptane, hexane, octane, etc.
While some of these latter are available in spectroscopically pure grades,
their purification for spectroscopic use may be readily achieved by passing
through a chromatographic column having silica gel (Grade I) in the lower
section and basic alumina (Grade I) in the upper section.
Similar purification procedures apply to cyclohexane, methylcyclohexane
and the decalins.
The purity of all these hydrocarbon solvents may be checked by gas-liquid
chromatography using an Apiezon, a Silicone oil or an SE-52 silicone rubber
gum chromatographic column.
https://en.wikipedia.org/wiki/Saturated_and_unsaturated_compounds
https://en.wikipedia.org/wiki/Aliphatic_compound
Aromatic Hydrocarbons
=========================
2) Benzene :
The analytical reagent grade benzene is satisfactory for most purposes;
if required dry, it is first treated with anhydrous calcium chloride , filtered
and then placed over sodium wire or a Type 5A molecular sieve.
Commercial benzene may contain thiophen C4H4S,
b.p. 84oC, which cannot be separated by distillation or by
fractional crystallization. The presence of thiophen may be detected by
shaking 3 ml of benzene with a solution of 10 mg of isatin in 10ml of
concentrated sulphuric acid and allowing the mixture to stand for a
short time : a bluish-green coloration is produced if thiophen is present.
The thiophen may be removed from benzene by shaking with concentrated
sulphuric acid, advantage being taken of the fact that thiophen is more
readily sulphonated than benzene. The technical benzene is shaken
repeatedly with about 15 percent of its volume of concentrated sulphuric
acid in a stoppered separatory funnel until the acid layer is colorless or
very pale yellow on standing, or until the thiophen test is negative. After
each shaking lasting a few minutes, the mixture is allowed to settle and
the lower layer is drawn off. the benzene is then shaken twice with
water in order to remove most of the acid, once with 10 percent sodium
carbonate solution, again with water and finally dried with anhydrous
calcium chloride. After filtration, the benzene is distilled through an
efficient column and the fraction, b.p. 80--81 oC, collected.
If required perfectly dry the distilled benzene may either be stored over
sodium wire or left in the presence of a Type 5A molecular sieve. Pure
benzene has b.p. 80oC/760 mmHg and m.p. 5.5 oC.
https://byjus.com/chemistry/aromatic-hydrocarbons/
Aromatic Hydrocarbons
===========================
3) Toluene :
Toluene free from sulphur compounds may be purchased. Commercial toluene
may contain methyl thiophens (thiotolenes), b.p. 112--113 oC, which
cannot be removed by distillation. It may be purified with concentrated
sulphuric acid in a similar manner to the purification of benzene, but care must
be taken that the temperature is not allowed to rise unduly ( <30 oC )
as toluene is sulphonated more easily than benzene. If required perfectly dry
the distilled toluene may be stored over sodium wire or left in the presence of
a Type 5A grade of molecular sieve. Pure toluene has b.p. 110.5 oC/760 mmHg.
4) Xylenes :
For solvent purposes various grades of xylenes (the mixture of isomers and
ethylbenzene) are available; purification and drying procedures are similar
to those used for benzene and toluene. For chemical purposes the commercially
available pure isomeric xylenes are usually available in at least 99 percent purity.
https://en.wikipedia.org/wiki/Aromatic_compound
Halogenated Hydrocarbons
=================================
5) Dichloromethane (methylene chloride) :
The commercial grade is purified by washing with 5 percent sodium
carbonate solution , followed by water, dried over anhydrous calcium
chloride and then fractionated. The fraction, b.p. 40--41 oC ,
is collected.
Methylene chloride is a useful substitute for diethyl ether in extraction
processes when it is desired to employ a solvent which is heavier than
water.
6) Chloroform :
The commercial product contains up to 1 percent of ethanol which is
added as a stabilizer. The ethanol may be removed by any of the
following procedures :
(a) The chloroform is shaken five or six times with about half its
volume of water, then dried over anhydrous calcium chloride
for at least 24 hours and distilled.
(b) The chloroform is shaken two or three times with a small volume
(say 5 percent) of concentrated sulphuric acid, thoroughly
washed with water, dried over anhydrous calcium chloride or
anhydrous potassium carbonate and distilled.
(c) The chloroform is passed through a column of basic alumina
(Grade I; 10 g per 14 ml of solvent), a procedure which also
removes traces of water and acid; the eluate may be used directly.
Pure chloroform has b.p. 61 oC/760 mmHg. It must not be dried
by standing with sodium or an explosion may occur. The solvent, when free
of alcohol, should be kept in the dark in order to avoid the photo-chemical
formation of dangerous quantities of phosgene.
https://www.sciencedirect.com/topics/earth-and-planetary-sciences/halogenated-hydrocarbon
7) Carbon Tetrachloride
============================
The analytical reagent product is sufficiently pure for most purpose;
the carbon disulphide content does not usually exceed 0.005 percent.
The technical product may contain up to 4 percent of carbon disulphide ;
this may be removed by the following method. One litre of commercial
carbon tetrachloride is treated with potassium hydroxide (1.5 times the
quantity required to combine with the carbon disulphide) dissolved in
an equal weight of water and 100ml of rectified spirit, and the mixture is
shaken vigorously for 30 minutes at 50--60 oC. After washing
with water, the process is repeated with half the quantity of potassium
hydroxide. Ethanol is then removed by shaking several times with 500ml
of water, followed by shaking with small portions of concentrated sulphuric
acid until there is no further coloration. The carbon tetrachloride is then
washed with water, dried over anhydrous calcium chloride and distilled.
Further purification may be effected , if necessary, by passing the distilled
solvent through a column of alumina and then allowing it to stand in the
presence of a Type 5A molecular sieve and finally distilling before use.
The pure compound has b.p. 76.5 oC/760 mmHg. Carbon
tetrachloride must not be dried over sodium , as an explosion may result.
Fire extinguishers containing this solvent cannot be applied to a fire
originating from sodium or similarly reactive metals.
Carbon tetrachloride is one of the solvents which may be dried relatively
efficiently by simple distillation, rejecting the first 10 percent of distillate,
until the distillate is clear.
https://en.wikipedia.org/wiki/Carbon_tetrachloride
Aliphatic Alcohols
=====================
8) Methanol :
The synthetic methanol now available is suitable for most purposes
without purification : indeed some manufacturers claim a purity of
99.85 percent with not more than 0.1 percent by weight of water
and not more than 0.02 percent by weight of acetone.
Most of the water may be removed from commercial methanol by
distillation through an efficient fractionating column ; no constant
boiling point mixture is formed as is the case with ethanol. Anhydrous
methanol can be obtained from fractionally distilled solvent by
standing over a Type 4A molecular sieve or by treatment with
magnesium metal using the procedure given for super-dry ethanol .
Pure methanol has b.p. 65 oC/760 mmHg.
If the small proportion of acetone present in synthetic methanol is
objectionable it may be removed when present in quantities up to
1 percent by the following procedure. A mixture of 500 ml of methanol,
25 ml of furfural and 60 ml of 10 percent sodium hydroxide solution is
refluxed in a 2-litre round-bottomed flask, fitted with a double surface
condenser, for 6--12 hours. A resin is formed which carries down all
the acetone present. The alcohol is then fractionated through an
efficient column, the first 5 ml which may contain a trace of formaldehye
being rejected. The recovery of methanol is about 95 percent.
https://en.wikipedia.org/wiki/Aliphatic_compound
Aliphate Alcohols
=====================
9) Ethanol :
Ethanol of a high degree of purity is frequently required in preparative
organic chemistry. For some purposes ethanol of ca. 99.5 percent purity
is satisfactory; this grade may be purchased (the "absolute alcohol" of
commerce), or it may be conveniently prepared by the dehydration of
rectified spirit with calcium oxide. Rectified spirit is the constant boiling
point mixture which ethanol forms with water, and usually contains
95.6 percent of ethanol by weight. Whenever the term rectified spirit is
used , approximately 95 percent ethanol is to be understood. Ethanol
which has been denatured by the incorporation of certain toxic additives,
notably methanol, to render it unfit for consumption, constitutes the
industrial spirit (industrial methylated spirit, IMS) of commerce; it is
frequently a suitable solvent for re-crystallization.
https://pocketdentistry.com/43-aliphatic-alcohols/
Dehydration of Rectified Spirit by Calcium Oxide
===================================================
Pour the contents of a Winchester bottle of rectified spirit (2--2.25 litres) into
a 3-litre round-bottomed flask and add 500 g of calcium oxide which has been
freshly ignited in a muffle furnace and allowed to cool in a desiccator. Fit the
flask with a double surface condenser carrying a calcium chloride guard-tube ,
reflux the mixture gently for 6 hours (preferably using a heating mantle) and
allow to stand overnight. Reassemble the condenser for downward distillation
via a splash head adapter to prevent carry-over of the calcium oxide in the
vapor stream. Attach a receiver flask with a side arm receiver adapter which is
protected by means of a calcium chloride guard-tube. Distill the ethanol gently
discarding the first 20 ml of distillate. Preserve the absolute ethanol (99.5%)
in a bottle with a well fitting stopper.
"Super-dry" ethanol :
--------------------------------------------------------
The yields in several organic preparations (e.g., malonic ester syntheses,
reductions involving sodium and ethanol, etc.) are considerably improved
by the use of ethanol of 99.8 percent purity or higher. This very high grade
ethanol may be prepared in several ways from commercial absolute alcohol
or from the product of dehydration of rectified spirit with calcium oxide.
The method of Lund and Bjerrum depends upon the reactions :
Mg + 2C2H5OH =>> H2 + Mg ( OC2H5 )2
Mg (OC2H5 )2 + 2H2O =>> Mg ( OH )2 + 2C2H5OH
Reaction (1) usually proceeds readily provided the magnesium is activated with
iodine and the water content does not exceed 1 percent . Subsequent
interaction between the magnesium ethanolate and water gives the highly
insoluble magnesium hydroxide; only a slight excess of magnesium is therefore
necessary.
Fit a dry 1.5- or 2-litre round-bottomed flask with a double surface condenser
and a calcium chloride guard-tube . Place 5 g of clean dry magnesium turnings
and 0.5 g of iodine in the flask, followed by 50--75 ml of commercial absolute
ethanol. Warm the mixture until the iodine has disappeared : if a lively
evolution of hydrogen does not set in, add a further 0.5 g portion of iodine.
Continue heating until all the magnesium is converted into ethanolate, then
add 900 ml of commercial absolute ethanol and reflux the mixture for
30 minutes. Distill off the ethanol directly into the vessel in which it is to be
stored, using an apparatus similar to that described for the dehydration of
rectified spirit. The purity of the ethanol exceeds 99.95 percent provided
adequate precautions are taken to protect the distillate from atmospheric
moisture. The super-dry ethanol is exceedingly hygroscopic; it may with
advantage be stored over a Type 4A molecular sieve.
If the alcohol is required for conductivity or other physico-chemical work and
traces of bases are objectionable, these may be removed by re-distillation
from a little 2,4,6-trinitrobenzoic acid. This acid is selected because it is not
esterified by alcohols, consequently no water is introduced into the alcohol.
Dehydration of rectified spirit by calcium oxide
=================================================
10) Propan-1-ol :
---------------------------------------
The purest available commercial propan-1-ol (propyl alcohol) should be
dried with anhydrous potassium carbonate or with anhydrous calcium
sulphate, and distilled through an efficient fractionating column. The
fraction , b.p. 96.5--97.5 oC/760 mmHg, is collected. If the
propan-1-ol is required perfectly dry, it may be treated with magnesium
activated with iodine by the method described above for ethanol.
11) Propan-2-ol :
--------------------------------------
Two technical grades of propan-2-ol (isopropyl alcohol) are usually marketed
having purities of 91 percent and 99 percent respectively. The former has a
b.p. of about 80.3 oC and is constant boiling point mixture with
water. Propan-2-ol may contain peroxide, which if present must be removed
before dehydration is attempted. Therefore test for peroxide by adding 0.5 ml
of propan-2-ol to 1 ml of 10 percent potassium iodide solution acidified with
0.5 ml of dilute ( 1 : 5 ) hydro-chloric acid and mixed with a few drops of starch
solution just prior to the test : if a blue ( or blue-black ) coloration appears in
one minute, the test is positive. To remove peroxide heat under reflux 1 litre of
propan-2-ol with 10--15 g of solid tin(II) chloride for half an hour. Test a portion
of the cooled solution for peroxide : if iodine is liberated, add further 5 g portions
of tin(II) chloride and heat under reflux for half-hour periods until the test is
negative. Add about 200 g of calcium oxide and heat under reflux for 4 hours,
and then distill, discarding the first portion of distillate. The water content may
be further reduced by allowing the distillate to stand over calcium metal or a
Type 5A molecular sieve for several days, followed by further fractionation.
Anhydrous propan-2-ol has b.p. 82--83 oC/760 mmHg; however,
peroxide generally redevelops during several days.
Dehydration of rectified spirit by calcium oxide
===============================================
12) Higher alcohols :
----------------------------------------------
These may be purified by drying with anhydrous potassium carbonate or
with anhydrous calcium sulphate, and fractionated after filtration from the
desiccant in apparatus with ground glass joints. The boiling points of the
fractions to be collected are as follows :
Butan-1-ol (butyl alcohol), b.p. 116.5--118 oC/760 mmHg.
2-Methylpropan-1-ol (isobutyl alcohol), b.p. 106.5--107.5 oC/760 mmHg.
Butan-2-ol (s-butyl alcohol), b.p. 99--100 oC/760 mmHg.
2-Methylpropan-2-ol (t-butyl alcohol), b.p. 81.5--82.5 oC/760 mmHg, m.p. 25.5 oC.
Petan-1-ol (amyl alcohol), b.p. 136--137.5 oC/760 mmHg.
3-Methylbutan-1-ol (isoamyl alcohol), b.p. 130--131 oC/760 mmHg.
Hexan-1-ol (hexyl alcohol), b.p. 156.5--157.5 oC/760 mmHg.
If perfectly anhydrous alcohols are required these may in general be
obtained by treatment with sodium followed by addition of the
corresponding alkyl succinate or phthalate. Sodium alone cannot be
used for the complete removal of water in an alcohol owing to the
equilibrium between the resulting sodium hydroxide and the alcohol :
NaOH + ROH ⇄ (reaction in both directions) ⇄ RONa _ H2O
The purpose of adding the ester is to remove the sodium hydroxide by
the saponification reaction :
CH2.CO2R CH2.CO2Na
l + 2NaOH --> l + 2ROH
CH2.CO2R CH2.CO2Na
Typically 7 g of sodium metal are added to 1 litre of butan-2-ol (having no more than
0.5% of water) contained in a two-necked flask fitted with a double surface condenser.
When all the metal has reacted (some warming may be necessary to increase the speed
of reaction), 33 g of pure 2-butyl succinate or 41 g of pure 2-butyl phthalate are added
and the mixture is heated under gentle reflux for two hours. Distillation through a
Vigreux column affords a distillate containing not more than 0.05 percent of water.
Dehydration of rectified spirit by calcium oxide
===========================================
13) Mono-alkyl ethers of ethylene glycol, R.O.CH2.CH2OH :
----------------------------------------------------------------------------------------------------------
The monomethyl, ethyl and butyl ethers are inexpensive and are known
as methyl cellosolve, cellosolve and butyl cellosolve respectively. They are
completely miscible with water, and are excellent solvents. The commercial
products are purified by drying over anhydrous potassium carbonate or
anhydrous calcium sulphate, followed by fractionation after the removal of
the desiccant. The boiling points of the pure products are :
Ethylene glycol monomethyl ether (or 2-methoxyethanol), b.p 124.5 oC/760 mmHg.
Ethylene glycol monoethyl ether (or 2-ethoxyethanol), b.p 1355 oC/760 mmHg.
Ethylene glycol monobutyl ether (or 2-butoxyethanol), b.p 171 oC/760 mmHg.
14) Mono-alkyl ethers of diethylene glycol, R.O.CH2.CH2.O.CH2.CH2OH :
--------------------------------------------------------------------------------------------------------------------------
The monomethyl, ethyl and butyl ethers are inexpensive commercial products
and are know as methyl carbitol, carbitol and butyl carbitol respectively. They
are all completely miscible with water and are purified as already described
for the "cellosolves" above . The boiling points of the pure compounds are :
Diethylene glycol monomethyl ether, b.p. 194 oC/760 mmHg.
Diethylene glycol monoethyl ether, b.p. 198.5 oC/760 mmHg.
Diethylene glycol monobutyl ether, b.p. 230.5 oC/760 mmHg.
Note :
The cellosolve and carbitol solvents may contain traces of peroxide.
These can be removed either by heating under reflux over anhydrous
tin(II) chloride (see 11. Propan-2-ol) or by filtration under slight
pressure through a column of activated basic alumina (Grade I);
the used alumina should be saturated with water before being
discarded.
https://en.wikipedia.org/wiki/Glycol_ethers
Ethers
============
15) Diethyl ether (Ether) :
-------------------------------------------------
The chief impurities in commercial ether (d. 0.720) are water and ethanol.
Furthermore, when ether is allowed to stand for some time in contact with air
and exposed to light, slight oxidation occurs with the formation of the highly
explosive diethyl peroxide, (C2H5)2O3.
The danger from this unstable compound becomes apparent at the conclusion
of the distillation of impure ether, when the comparatively non-volatile
peroxide becomes concentrated in the residue in the distillation flask, and a
serious explosion may then result if an attempt is made to evaporate the
ether to dryness. It is perhaps worthy of comment in this connection that in
the extraction of an organic compound with ether and the subsequent
removal of the solvent, the presence of the residual compound seems largely
to eliminate the danger due to traces of peroxide, due presumably to its
catalytic effect which leads to a more controlled decomposition. Nevertheless
ether which has been standing for several months in a partially filled bottle
exposed to light and air should be tested for peroxide by the procedure
described under [11] Propan-2-ol. If present, the peroxide may be removed
by shaking 1 litre of ether with 10--20 ml of a concentrated solution of an
iron (II) salt prepared either by dissolving 60 g of iron(II) sulphate in a
mixture of 6 ml of concentrated sulphuric acid and 110 ml of water, or by
dissolving 100 g of iron(II) chloride in a mixture of 42 ml of concentrated
hydrochloric acid and 85 ml of water.
Peroxide may also be removed by shaking with an aqueous solution of
sodium sulphite or with solid tin(II) chloride (see[11] Propan-2-ol) or by
passage through a column of alumina. It is worthy of note that all dialkyl
ethers have a tendency to form explosive peroxides and they should be
routinely tested before further purification leading to a final distillation
process is attempted.
Apart from the dangers inherent in the use of diethyl ether due to the
presence of peroxide, attention must be directed to the fact that ether
is highly inflammable and also extremely volatile (b.p. 35oC), and
great care should be taken that there is no naked flame in the vicinity
of the liquid. Under no circumstances should ether be distilled over a
bare flame, but always from a steam bath or an electrically heated
water bath and with a highly efficient double surface condenser.
Ether vapor has been known to ignite on contact with a hot plate or
even a hot tripod upon which a water bath has previously been heated.
https://en.wikipedia.org/wiki/Ether
Ethers :
==================
16) Di-isopropyl ether :
--------------------------------------------
The commercial product usually contains appreciable quantities of
peroxide; this should be removed by treatment with an acidified
solution of an iron(II) salt or with a solution of sodium sulphite
(see [15] Diethyl ether). The di-isopropyl ether is then dried over
anhydrous calcium chloride and distilled,
the fraction b.p. 68.5 oC/760 mmHg being collected.
17) Dibutyl ether :
------------------------------------------------
Technical dibutyl ether does not usually contain appreciable quantities
of peroxide, unless it has been stored for a prolonged period. It should ,
however, be tested for peroxide , and, if the test is positive , the solvent
should be shaken with an acidified solution of an iron(II) salt or with a
solution of sodium sulphite (see under [15] Diethyl ether). The dibutyl
ether is dried with anhydrous calcium chloride and distilled through a
fractionating column : the portion b.p. 140--141 oC is
collected. If a fraction of low boiling point is obtained, the presence of
butan-1-ol is indicated and may be removed by shaking twice with an
equal volume of concentrated hydrochloric acid , followed by washing
with water and drying . Pure dibutyl ether has b.p. 142 oC/760 mmHg.
Ethers
===========
18) Di-alkyl ethers of monoethylene and diethylene glycol :
--------------------------------------------------------------------------------------------------------
The dimethyl ether of ethylene glycol (dimethoxyethane CH3.O.CH2.CH2.O.CH3 ,
frequently referred to as DME or dimethyl cellosolve or glyme) has
b.p. 85 oC/760 mmHg, is miscible with water, is a good solvent
and an excellent inert reaction medium. The diethyl ether of ethylene glycol
(diethyl cellosolve) is partially miscible with water (21% at 20 oC) and has
b.p. 121.5 oC/760 mmHg.
The dimethyl ether of diethylene glycol (CH3.O.(CH2.CH2.O)2CH3 ,
diglyme has b.p. 62 oC/17 mmHg; the corresponding diethyl ether (diethyl carbitol)
has b.p. 186 oC/760 mmHg.
All these are excellent solvents for organic compounds; they are purified
by initial storage over sodium hydroxide pellets and then heated under
reflux with calcium hydride, lithium aluminium hydride, sodium hydride, or
sodium , before being fractionally distilled (under reduced pressure if
necessary) in an atmosphere of nitrogen.
19) Tetrahydrofuran :
-------------------------------------------
The commercial grade of this solvent is obtainable in greater than 99.5 percent
purity, in which water and peroxides are the major impurities; an inhibitor for
peroxide formation may have been added by the manufacturers. Peroxide, if
present, must be removed by passage through a column off alumina, or by
shaking with iron(II) sulphate solution as described under diethyl ether before
drying and further purification is attempted. If the latter method is employed the
solvent should then be dried initially over calcium sulphate or solid potassium
hydroxide, before being heated under reflux over calcium hydride or lithium
aluminium hydride. The solvent is finally fractionally distilled. Pure tetrahyrofuran
has b.p. 65--66 oC/760 mmHg; it should be stored over calcium hydride.