Org. Synth. 1947, 27, 43
DOI: 10.15227/orgsyn.027.0043
[Valeraldehyde, δ-hydroxy-]
Submitted by G. Forrest Woods, Jr.
Checked by Cliff S. Hamilton and Wm. V. Ruyle.
1. Procedure
In a 1-l. three-necked flask provided with a Hershberg stirrer are mixed 300 ml. of water, 25 ml. of concentrated hydrochloric acid (Note 1), and 100 g. of 2,3-dihydropyran (p. 276). The mixture is stirred until the solution has become homogeneous and then for an additional 20 minutes (Note 2). After the addition of a few drops of phenolphthalein indicator to the mixture, the acid is neutralized with 20% sodium hydroxide; enough alkali is added so that a faint pink color just persists.
The solution is then transferred to a continuous extractor and extracted with ether for about 16 hours. The ether extract is added in convenient portions to a 250-ml. modified Claisen flask fitted with a condenser and a suitable fraction-cutter for distillation under reduced pressure. The ether is removed by distillation under the diminished pressure of a water pump, and the residue is then distilled at about 10 mm. pressure. After a small fore-run which weighs 2–5 g., the product distils as a clear, colorless, viscous oil at 62–66°/9–10 mm.; n25D 1.4513. The yield is 90–95 g. (74–79%) (Note 3) and (Note 4).
2. Notes
1. The quantity of acid is arbitrary. This amount was chosen to minimize the time of hydration. The order of addition of the reactants should be that stated above. Less acid may be used with increased reaction time; more should not be used.
2. About 5–10 minutes is required before the solution becomes homogeneous. Some heat is evolved during the hydration. The submitter has found that the amount of 2,3-dihydropyran may be increased up to 300 g. without using more water or acid; however, if larger quantities of the pyran are used, the pyran must be added dropwise to the acid solution with cooling.
3. A convenient apparatus for the distillation is a modified Claisen flask whose side arm is provided with a short water-cooled condenser. A fraction-cutter of the "pig" type is satisfactory.
4. According to the submitter the product can be converted smoothly to pentamethylene glycol by hydrogenation over Raney nickel at 90° and 2000 lb. pressure. It will also undergo reductive alkylamination by a procedure similar to that described for 2-isopropylaminoethanol (p. 501).
3. Discussion
5-Hydroxypentanal has been prepared only by the method of Paul,1 of which the above is an adaptation.

References and Notes
  1. Paul, Bull. soc. chim. France, (5), 1, 976 (1934).

Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

hydrochloric acid (7647-01-0)

ether (60-29-7)

sodium hydroxide (1310-73-2)

Raney nickel (7440-02-0)

pentamethylene glycol (111-29-5)

phenolphthalein (77-09-8)


Valeraldehyde, δ-hydroxy- (4221-03-8)

2-isopropylaminoethanol (109-56-8)