Org. Synth. 1954, 34, 71
DOI: 10.15227/orgsyn.034.0071
3-METHYL-1,5-PENTANEDIOL
[1,5-Pentanediol, 3-methyl-]
Submitted by Raymond I. Longley, Jr. and William S. Emerson
1.
Checked by T. L. Cairns and John F. Harris, Jr..
1. Procedure
In a
2-l. three-necked flask equipped with a stirrer and thermometer are placed
336 g. (2.62 moles) of 3,4-dihydro-2-methoxy-4-methyl-2H-pyran (
p. 311), 630 ml. of water, and
24 ml. of concentrated hydrochloric acid (sp. gr. 1.19). The mixture is stirred for 2 hours, during which the temperature may reach 50° but should not be permitted to rise higher. Solid
sodium bicarbonate is then added until the solution is neutral to pH indicator paper
(Note 1). The entire reaction mixture weighing about 1 kg. together with
39 g. of Raney nickel2 is introduced into a
3-l. stainless-steel rocking hydrogenation autoclave. A
hydrogen pressure of at least 1625 p.s.i.
(Note 2) is applied, and the autoclave is heated to 125° and held there with shaking for 4 hours. The mixture is allowed to cool overnight, and the catalyst is separated either by suction filtration through Filter-Cel or by centrifugation. The solution is distilled through a
12-in. Vigreux column. After the
methanol and water are separated, the
3-methyl-1,5-pentanediol distils at
139–146°/17 mm.,
149–150°/25 mm. The yield is
251–256 g. (
81–83%),
n25D 1.4512–1.4521.
2. Notes
1.
The submitters report that
β-methylglutaraldehyde may be isolated at this point from an analogous hydrolysis. The hydrolysis is carried out with
196 g. of 3,4-dihydro-2-methoxy-4-methyl-2H-pyran in 650 ml. of water and
15 ml. of concentrated hydrochloric acid for 3 hours. After neutralization with
sodium bicarbonate, the solution is saturated with
sodium chloride and extracted continuously with
ether for 20 hours. The
ether is removed by distillation, and the product is dried thoroughly by azeotropic distillation using a
benzene-hexane mixture. Distillation affords
β-methylglutaraldehyde, b.p.
85–86°/15 mm.,
n25D 1.4307–1.4351. Yields up to
90% have been secured. The aldehyde polymerizes on standing but is stable as a 50% solution in water or
ether. The monomer may be recovered by careful destructive distillation of the polymer.
2.
The initial
hydrogen pressure should be high enough that it does not fall below 1000 p.s.i. during the shaking period.
3. Discussion
3-Methyl-1,5-pentanediol has been prepared by the hydrogenation of
ethyl β-methylglutarate;
3 by the hydrogenation of
ethyl β-methyl-α,γ-dicarbethoxyglutarate;
4 by the hydrogenation of
β-methylglutaraldehyde;
5 and by heating
3,4-dihydro-2-methoxy- 4-methyl-2H-pyran with water,
hydrogen, and
copper-chromium oxide,
nickel on kieselguhr,
5 or
Raney nickel catalyst.
6
This preparation is referenced from:
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
3,4-dihydro-2-methoxy- 4-methyl-2H-pyran
hydrochloric acid (7647-01-0)
methanol (67-56-1)
ether (60-29-7)
hydrogen (1333-74-0)
sodium bicarbonate (144-55-8)
sodium chloride (7647-14-5)
nickel,
Raney nickel (7440-02-0)
Copper-Chromium Oxide
benzene-hexane (1077-16-3)
3,4-Dihydro-2-methoxy-4-methyl-2H-pyran (53608-95-0)
3-Methyl-1,5-pentanediol,
1,5-Pentanediol, 3-methyl- (4457-71-0)
β-Methylglutaraldehyde (6280-15-5)
ethyl β-methylglutarate
ethyl β-methyl-α,γ-dicarbethoxyglutarate
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