BASICITYOF SUBSTITUTED ACETOPHENONES
Dec. 5, 1958 TABLE VI11 EQUILIBRIUM CONCENTRATIONS O F
KETALSWITH
VARIOUS
6355
B y differentiating equation ’7, simplifying, and setting equal to 1 (because maximum separation can be obtained when dy/dx = 1) we get
2,2-DIMETHYL-1,3-PROPANEDIOL-KETONERATIOS Equil. concn. of cyclohexanone ketal
Equil. concn. of 2-methylcyclopentanone ketal
1 2
0.57
1
3
.82
1 1
4 4.5
.86 .88
0.03 .06 .09 .11 .12
Init. concn. of dicarbonyl cpd.
1 1
Init. concn. of giyc01
.75
Substituting for y in ( 5 ) and solving for x , we get ~3 - 5.041~’ 6 . 1 2 2 ~- 2.011 = 0
+
(8) This equation was solved b y Homer’s method’o t o yield a value x = 0.573, which leads t o a value of 0.026 for y . I n a similar way calculations can be made for other initial glycol concentrations. In Table VI11 a few of these results are listed. (20) I. S. a n d E. S. Sokolnikoff, “Eligher hlathematics for Icngineers a n d Physicists,” hIcCraw-€IIill Book Co., Inc., New U o r k , N. Y., 1!134. pp. 27-32,
[COSTRIBUTION FROM
THE
(9)
O n solving, Tve find t h a t
x = 0.88 and y = 0.12.
In order t o find out what initial glycol concentration Tvould be required t o obtain maximum separation, substitute the following values in equation 3 initial ketone concentration 1 initial glycol concentratiou cyclohexanone ketal concri. a t equil. 0.88 0.12 = 1.00 0.88 water concn. a t equilibrium 1.00 - 0.88 = 0.12 cyclohexanone concn. a t equil. -” _ 1 glycol coiicn. a t equilibrium
+
On solving we find t h a t z = 4.3 and hence maximum preferential blocking can be obtained when 4.5 moles of 2,2dimethyl-l,3-propanediol is equilibrated with one mole of the hypothetic diketone A. COLUMBUS
10, OHIO
DEPARTMEST OF CHEMISTRY, UNIVERSITY OF BRITISHCOLUMBIA]
The Protonation of the Carbonyl Group. I. The Basicity of Substituted Acetophenones BY Ross STEWART AND K. UATES’ RECEIVED JGLY 9, 1958 T h e basicities of twenty 1 ) and ~ p-substituted acetophenones have been determined by a spectrophotometric mcthoti ill sulfuric acid media. With the exception of hydroxy and alkoxy groups which, i t is believed, hydrogel1 bond strongly t o tlic ~ + Y( =(,, solvent, a very good correlation exists between pKH1%+ and u+. .I good correlation also csists betweeii p k - ~ and t.he carbonyl stretching frequencies in the ketones. The conjugate acid of 2-acetylfluorene is considerably niore stable than t h a t for P-phenylacetophenone and the theoretical consequences of this are discussed.
I n connection with a study of the position of protonation of the carboxyl group, which will be reported later, we found it necessary to use compounds containing the carbonyl group as models. The protonation of the carboxyl group might occur a t either the “carbonyl” or “ether” oxygen but there is one oxygen atom only available for protonation in a carbonyl compound. IYe have accordingly determined the effect of nz- and psubstituents on the basicity of acetophenones and this information later will be correlated with the data obtained with substituted benzoic acids. Hammett3a-bacin his classical investigation of the strength of very weak bases determined the basicity of acetophenone and its p-CH, and p-Br derivatives by a spectrophotometric method in sulfuric acid solution. This approach, which we have followed, utilizes the concept of the E10 acidity function and has the advantage of producing absolute values of basicities, ;.e., absolute insofar as they are based on dilute aqueous solution as the standard state. Pratt and Matsuda4 determined relative basicities of some acetophenones in benzene solution by a dis(1) Presented a t t h e S a n Francisco Meeting of t h e American Chemical Society, April 7-11, 1958. (2) Holder of a National Research Council of C a n a d a Studentship, 1‘3:57-1938. (3) (a) I.. A. Plexser. L. P. H a m m e l t and A. Dingwall, ’Tiirs J O I J K N A I . . 61,2103 (1935); (b) L . A. Ilexser and I,. P. Hanitnett, i b i d . , 60, 885 (1938): (c) L. P. H a m m e t t a n d A . J . Deyrup, abid.,64, 2721 (1932). (4) E . F. P r a r t a n d K. M a t s u d a , ibid., 1 6 , 3739 (1953).
tillation method. They obser p-Ohle and p-OEt have anomal
Experimental Acetophenones.-Commerciallv
availabic acetophenimcs were purified either by vacuum distillation or by several recrystallizations. i?z-hleth~lacetophenoiie was prepared froin ?)i-broinotoluene b y the method of Gilman and Se1son.j m-Chl(iroand nz-bromo-acetophenones were obtained by diazotization of nz-aminoacetoplienone followed by the standard Sandmeyer procedure. p-Fluoroucetophenone and %-acetylfluorene were prepared by the standard Friedel-Crafts acylation of fluorobenzene and fluorene, respectively. The physical constants of t h e purified compounds are reported in Table I. Sulfuric Acids .-Sulfuric acid-water solutions ranging from 44.0 to 95.5$, acid were prepared b y dilution of Fisher C.P. Reagent grade sulfuric acid (95.0% min.). Concentrations mere determined by titration with standard base. The HOvalues of these were obtained by interpolation from a standard curve constructed using the values given b y Paul and Further solutious up t o pared from 30y0 fuming sulfuric acid (Baker and Adamson reagent) and H O values of these determined by indicator methods.3c All HOvalues of solutions were checked periodically. Measurement of ~KBH+.--;\sample of each ketone weighed on a microbalance was dissolved in acetone t o make a 5 X JILT stock solution from which 0.1-ml. aliquots wcre pipetted into standardized 10-ml. \-olumetric flasks. After the acetone had been removed a t the pump, the flasks were made up t o volume with the sulfuric acid-water mixtures, the resulting concentration of lietonc being 5 X 10-5 ( 5 ) H. Gilman and J. F. Nelson, Rec. Iraa. d z i i i i , , 66, 520 (1936) (G) M. A. Paul and F. A. Long, Chem. Revs., 67, 1 (1957).
6356
Ross STEWART AHD K. YATES
.If. I n cases of sullicierit water soluldity, aqueciui ytock solutions were prepared and t h e acids added directll- t o the aliquots, eliminating removal of solvent and possible loss of ketone by evaporation. Necessary corrections were made for :idded water. The flasks were then maintained a t 23 i (1.1O h>-means of n constant temperature bath. 'l'ltc estinctiou coeL5cients of the :ibove solutions were cletiriiiiiied a t two TvaT-e lengths Tritli quartz cells of 1-cm. 1);itli length using a Beckmnn model L)U spectrophotometer ~ ~ l i o ccll i c compartment was iiiaintained at the above temi)er;tture by means of therniospacers. The sulfuric acids \vc'i-c tested for optical clarity in t h e regions used and a \I il\-ent blank of the same conceiitr:ttion as t h a t containing t11r ketone nl1.s used. rltraviolet absorption spectra of tlic ketones in 44.0ri anti 95.jC; acids measured with a G i i - b - inodcl 14 recording spectropliotoincter were used where iry to 1oc:tte t h e wave letigtlis o f iiiasinial absorption ( i f the unprotnnntetl (Xu) criitl prvtoii:ttctl ( X i ) forms. Thew :,rc>liitcd itt Tithle IT.
~ K B HA~S D-
\\-AVE
Vol.
T A B L E 11 LESCXII1 f A X I X 4
FUR
so
SCBSTI'IUTEL)
ACETOPIIESOSES ( 1l.O%
Substituent
ti.15 02
2,70
ti
P-CH?
:,
P-CsHs Ilt-OCHz
.7.61 ii 717 4 81 ii 70
p-OC2Hj iwOH
I
mu
H" iit-CH~
p-OCHa ?12-oc?I-rj
,
1,!Ill
p-OH p - I: 112-Cl p-cl iii-Br />-Drb
;.01 6 .52 ti. Ill! t i . 52
,%SO: d- CAI1 p-C61-Ti 2,3 -C :€I67
7 ii' 7 il-l
