and Anna S. Naff Dickinson College Carlisle, Pennsylvania
I
Recyclization Apparatus for Esterification
The direct reaction of an alcohol with an organic acid will lead in time to an equilibrium mixture. RCOOH
+ ROH 8 R-&OR II
+ H20
0
Berthelot and PBan de St. GillesZ(1862) found that an excess of either reactant favors ester formation. 11lustrative data is given in Moewlyn-hug he^.^ Alternatively, the yield of ester may he increased by removal of one of the products of the reaction. The readily available alcohols: n-butyl, iso-butyl, and n-amyl alcohol form minimum boiling ternary azeotropes of the alcohol, acetate ester and water in which the water content is 30% or more.< (See Table 1.) Moreover, when these azeotropes condense each separates into an organic-rich phase and essentially pure water. .
Robertson and Jacobs5 describe a method for preparing n-butyl acetate which employs the minimum boiling azeotropes of water, hutyl alcohol, and hutyl acetate to remove water from the esterification reaction. Their experimental method consists of fractionally distilling the crude azeotrope from a hutyl alcohol-excess acetic acid reaction mixture. The distill* tion is interrupted several times in order to return the upper layer of the condensate, an alcohol-ester rich layer, to the reaction flask, thus forcing the reaction to approach completion. We have devised a simple apparatus which avoids these periodic interruptions in distillation and allows the esterification essentially to he completed with a minimum of effort and in a manner which is instructionally valuable. The Equipment
The equipment for the esterification reaction is shown in the figure. It consists of a two-necked, 250ml, round-bottomed flask fitted vertically with a fractionating column (condenser packed with stainless steel wool). A simple distillation adapter holding a thermometer is seated in the top of the condenser and connected to a water-cooled condenser set for down-
Recydizotion apparatus for erterification reactions
680 / Jowml of Chemical Education
'For reprints address 75 Three Mile Road, Cold Spring, Kv. ' BERTHELOT, M. P. E., and PBANDE SAINTGILLE,L., Ann. Chim. phys., 66,5 (1862); 68,225 (1863). a MOEWLYN-HUGHES, E. A,, "Physical Chemistry," Pergamon Press (Znd reu. ed.), Oxford, 1961, p.,1022. W o w Chemical Co.. "Aaeotro~lcData." American Chemical Society, Advances in chemistry ~eries,1952. T. L.. "Laboratorv Practice ROBERTSON. R. G.. AND JACOBS. of Organic ~h&nistr{," (4th ed.), ' ~ a c & i l l a nCo., ~ e York, w 1962, p. 227.
Table 1.
Alcohol n-hutyl alcohol
iao-hutyl alcoho
Minimum Boiling Azeotropic Mixtures of Water, Alcohol, and Ester
First Water hp 100°C Wster Water lu-butyl alcohol Water Water Water
n-amyl alcohol
Water Water Water
Component Second n-hutyl alwhol bp 1 1 7 . 4 T n-butyl alcohol n-butyl acetate n-butyl acetate iso-butyl alcohol hp 1 0 7 T iso-hutyl alcohol iso-butyl acetate iso-butyl alcohol n-amyl alcohol hp 1 3 7 . 8 T n-amyl alcohol n-amyl alcohol
ward distillation. The end of the water cooled condenser juts into an inverted Claisen head which is clamped as shown in the figure. The bottom end of the straight side of the Claisen head is fitted with a stopper, tubing, and pinch clamp for draining the water formed in the condensate. In normal operation an alcohol-rich upper layer overflows into the downward bent sidearm of the Claisen head and is conveyed back to the reaction flask by a tubing system. The short rubber tubing linkage in this system contains a glass bead for controlling the return rate of flow. This bead is essential for the proper operation of the apparatus. The Experiment
Recyclization method. The reaction conditions are essentially those of Robertson and Jacobs. To a thoroughly mixed solution of 0.6 mole acetic acid and 3 ml conc. sulfuric acid in the reaction flask are added 0.5 mole n-butyl alcohol and a few boiling stones. The flask is swirled vigorously to mix the reactants and the apparatus assembled. The contents of the flask are gently refluxed for 10 min, then the rate of heating is adjusted so the temperature a t which distillation proceeds is no more than 2'C above the boiling point of the water-alcohol azeotrope. (See Table 1.) When the azeotrope is collected in the receiver, an inverted Claisen head, it separates into two layers, the water layer on the bottom and the organic layer on the top. I n a short time, the top layer begins to flow into the return tube and is fed a t a uniformrateto the reaction flask by the experimenter pinching the rubber tubing over the glass bead. Thus, the temperature of the pot contents may be kept nearly constant and controlled for optimum fractionation of the distillate. The water level in the receiver is allowed to rise to a point short of permitting it to be carried back mechanically to the reaction flask. Excess water is drained into a graduate. Distillation is continued until no water is observed to separate from 10 to 15 drops of distillate. Then the rate of heating is increased and distillation continued until the boiling point range of the ester is reached. 8 Washing the reaction mixture with water prior to extracting with carbonate greatly reduces the possibility of mechanical loss of the product. After filtration, care must he taken to press the drying agent free of ester. Considerable loss of product can occur at this point. Qee footnote 5.
'
"C hp of Azeotrope
Third n-hutyl acetate bp 126.2'C
iso-butyl acetate hp 117.2"C
d% of &st Component
89.4
37.3
92.7 90.2 116.2 86.6
42.5 28.7 73.3 30.4
89.8 33 87.4 16.5 Nonazeotropic 94.8 56.2
iso-butyl acetate n-amyl acetate bp 148.8-C
95.8 54.4 Nonaaeotropic Nanazeotropio
w m y l acetate n-amyl acetate
If alcohol remains unreacted, the alcohol-ester azeotrope or alcohol distills a t a constant temperature b e low the boiling point of the ester. Should this occur, the heat input must be decreased and collection of the lower-boiling azeotrope continued. After the reaction is complete, the water layer is drained into a graduate, and the organic layer returned manually to the reaction flask. The reaction mixture is cooled to room temperature, washed with 25 ml ice water: then very cautiously with 30 ml of saturated sodium carbonate. The product should be tested with litmus to be sure it is not acidic. Finally, the product is washed with 25 ml of water and dried over 6-8 g anhydrous magnesium sulfate.? The n-butyl acetate is distilled and the fraction boiling between 12&126°C collected. Equilibrium method. The reaction conditions are the same as described above except the flask is fitted with a simple reflux condenser. The reflux time is 30 m h 8 The reaction mixture is washed first with water, then with carbonate. Extreme care must be taken in washing the reaction mixture with carbonate as this mixture contains much unreacted acid. Following the carbonate wash, the product is extracted with 25 ml saturated calcium chloride to remove any unreacted alcohol. Results
The reaction time under recycliiation conditions is about forty-five minutes. A comparison of the yield of the two different methods is shown in Table 2. The method described was found to be unsatisfactory for the preparation of esters of n-propyl acetate or iso-propyl acetate. The reason for this is the low water content of the corresponding azeotrope and the high solubility of the ester in water. With iso-amyl acetate, a high boiling material is formed that reduces the yield of ester. Table 2.
Esterification Reaction.
--
Comparison of Results
Yield (%+ Reeyclization Equilihrrum Com~ound Method Method n-hutyl acetate iao-butyl acetate n-amyl acetate
Ester bp 'C ranee
67f 3%
5 6 . 3 1 1.7%
120-126
68 1 3 %
58
+l'%
112-118
72 1 2%
62.5f 2.5%
14P150
Volume 44, Number 11, November 1967
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