The Ionization Constant of Para Cyanobenzoic Acid Citation Valby, Edgar Peterson (1926) The Ionization Constant of Para Cyanobenzoic Acid. Bachelor's thesis, California Institute of Technology. doi:10.7907/ZFK9-ZQ29. https://resolver.caltech.edu/CaltechETD:etd-12062004-145203 Abstract No abstract. Item Type: Thesis (Bachelor's thesis) Subject Keywords: Chemical Engineering Degree Grantor: California Institute of Technology Division: Chemistry and Chemical Engineering Major Option: Chemical Engineering Thesis Availability: Public (worldwide access) Research Advisor(s): Unknown, Unknown Thesis Committee: None, None Defense Date: 1 January 1926 Record Number: CaltechETD:etd-12062004-145203 Persistent URL: https://resolver.caltech.edu/CaltechETD:etd-12062004-145203 DOI: 10.7907/ZFK9-ZQ29 Default Usage Policy: No commercial reproduction, distribution, display or performance rights in this work are provided. ID Code: 4812 Collection: CaltechTHESIS Deposited By: Imported from ETD-db Deposited On: 08 Dec 2004 Last Modified: 03 Oct 2019 23:38 Thesis Files Preview PDF (Valby_ep_1926.pdf) - Final Version See Usage Policy. 593kB Repository Staff Only: item control page

fhe IONIZATION CONSTANT of PARA CYANOBENZOIC ACID Thesis by Edgar P. Valby In partial fulfillment of the requirements for the degree of Bachelor of Science in Chemical Engineering. CALIFORNIA INSTITUTE OF TECHNOLOGY Pasadena, California 1926 THE IONIZATION CONSTANT OF PARA~CYANO-BENZOIC ACID. PURPOSE The purpose of this research was to determine the and ionization constant K, of p-cyanobenzoic acid,its position in the para substituted benzoic acid series. THEORY Since the ionization constant of the para substi- tuted benzoic acids is a measure of the electron attrac- tion of the substituting radical, it was necessary to determine the Ky of pecyanobenzoic acid in order to place the cyanide radical in this scheme. | According to the Mass Law the expression HX > HYt KX. e(1 -y) cy cy = for 7 ~ Kp must hold, where 7 is the | amount ionized and c is concentration in mols per liter. It is known that Ax: y=amount ionized , where ‘A. is the equivalent conductance of the acid at a known con- centration ana ~\,, the equivalent conductance at infinite dilution. The problem then resolved into preparing the pure acid and measuring the conductance of known concentration of the acid. PREVIOUS WORK. No reference could be found in the literature to the K, of p-cyanobenzoic acid, probably because Sandmeyer’ reported that it was unstable and changed into " terephthelamide upon crystallization from hot water. However, Kattwinkel and Wolffenstein- showed that pecyano benzoic acid is stable,and can be prepared by the Sandmeyer reaction from p-aminobenzoic acid. It has a MP. of 219°C. and crystallizes in white plates. These investigators report no yielde. EXPERIMENTAL METHODS and RESULTS. The experimental work carried out was the prepa- ration of p-nitrobenzoic acid, the peaminobenzoic acid, and p-cyanobenzoic acid, which was purified and used for conductivity measurements... Preparation of P-nitrobenzoic Acid. The procedure given in Organic Syntheses was used. Three batches were run. 200 gm. 72% yield. 180 * 65% * 5 oe 206 * (Wohn Akers) 74% (1) Sandmeyer 8B. 18, 1497 (1885). (2) Kattwinkel and Yolffenstein B. 34,2423 (1901) (3) Organic Syntheses Wiley. Vel. IT p. 53. wae Preparation of P-aminobenzoic Acid. Vilbrand and Beilstein’, and Vanino” reduced the nitro compound with Tin and Hydrochloric acid, but give no yields. The method finally adopted here was to mix 150 grams p-nitrobenzoic acid and 320 grams tin in a 5 ii. ballon flask. Then 350 ¢.c. of conc. HCl were added ‘in small portions. It is advisable to add hot dilute HCL at first so that the reaction can be started under ‘control. If too much conc. HCL is added at first, the reaction becomes too violent. When the reaction was completed the solution was evaporated to dryness, the mass treated with conc. NH,OH and the stannous oxide filtered off. The ammonia solution was boiled to remove the excess ammonia, acidified with acetic acid, and | allowed to crystallize. The crystals were filtered off _and,after they were recrystallized from hot water, came out as brown needles. a Yield (75 gm.) 60 %. M.P. 182-183 C. (unc.) (4) Wilbrand and Beilstein A. 128, 262 (1863). (5) Vanino,p.573, “Braparative Chemie" (Enke) Vol.2 (1993) p. 573. (4n this method the chloride of peaminobenzoic acid crystallizes out.) ohm Fischer” reduced the p-nitrobenzoic acid with H2S in an ammoniacal solution. This was tried in the follow- ing manner. Ten gm¢é. p-nitrobenzoic acid was dissolved in 125 cc. dilute NHyOH and HyS was passed in until the solution was saturated. It was then heated and more gas introduced until a red brown color developed. The flow of H25 was discontinued and the solution evaporated until the color changed to yellow. -The sulfur formed was fils tered off; the solution acidified with acetic acid; evaporated to 50 cc. , and set aside to cool. Yellow erystals formed. These were all soluble in NaOH but not completely soluble in HCl, thus showing that some unchanged p-nitrobenzoic acid was present. The product, recrystallized from hot water, formed long yellow needles. Yield (4.3 gms.) 53%. M.P. 181.5-182.5 ¢ (une). This procedure is less difficult than the. one in which tin and HCl are used. Preparation of P-cyanobenzoic Acid. Kattwinkel and Wolffenstein~ found that pecyano- benzoic acid existed, had a M.P. of 219 C and crystallized from hot water in white plates. Hantech” showed that syn and anti forms of the N=N-CN radical exist; of which the (6) Fischer A. 127, 142 (1863). (7) Hantech 2B. 28, 666 (1a98). o5= anti is stable and will not enter into the Sandmeyer reaction. Sarl D. Stewart’ found that the stable form could be prevented by having the cuprous cyanide solution in the Sandmeyer reaction alkaline with Na,C0;. Using Stewart's idea the following procedure was devised. p COOHG HyNE, +NaNO, +2HC1 =p COOHG,H, KCl +NaCl+2H 0. p COOHG,H,X,Cl 4CuCN = p COORG, HCN + CuCl. tobine Cuty solutio Ce eenda to the direction To; nyaccording 8 given in Organic Syntheses’ was added 60 gms. HazC0; (anhydrous)... The diezotized solution was prepared by treating a mixture of 40 gm. p-eaminobenzoic acid in 61 cc. cone. HCl (C.P.},100 ec. water cooled with 300 gm. ice ; with 20 gn. sodium nitrite in 50 cc. water until a starch iodide wes positive. Then the diazotized solution was added to the CuCN solution at an average temperature of 50-60 C with an active evolution of gas. When the gassing stopped, the solution was acidified with HCl1,(slowly), the — “precipatated CuCN and pecyano benzoic acid were filtered offfand washed. The solid was treated with about 75 cc. of conc. NH/OH arid filtered. The filtrate was acidified with HCl, precipatating the p-cyanobenzoic acid as a (8) Earl D. Stewart Senior Thesis California Institute of Technology. 1925. (9) Organic Syntheses Vol. yp. 53. Vol.wWp. 69. brown mass. Yield crude 45 %. M.P- 106-110 C.(unc.) The product was purified by treating its hot water solution 5 times with prepared charcoal. This treatment gave a pure product of white plates. Yield (13 gms.) 30% M.P. 218.5-219°C (cor.) Its solubility was found to be about .12 grams in 100 ec. of water at 20 C, and about 4 gms. at 100°C. DERTERMI NATION ‘of IONIZATION CONSTANT. The relations used in determining the conductivity of the solution are: —h-: k :cell constant FF =specific conductance L-=acutal conductance > A. = 1000 L .~ 100k c c ~ ec oR /A\ sequivalent conductance R-actual resistance c= concentration in mols per liter Thus R is the only value to be measured. This can Measurtt9 be determined by,the resistance of a known solution by the Kohlrausch method, using, however, an A C galvanometer for detecting balance instead of a telephone receiver. ~Fu EXPERIMENTAL DATA Conductivity Cell #5. kk .186 Temp. 26 C, Number Concentration hesistance | 1 007446 N 352.9 Ohms 70.8 2 .006936 267.5 93.6 3. .006909 369.6 72.8 4 004141 494.0 90.9 5 -002059 758.3 119.6 6 .0008235 1347.0 167 .6 Since the amount of ionization _ Ac 71> No the values of K, can be calculated from the formula z c - atin =Ka- A, ~f\Ht+AX, An examination of the known equivalent conductances of the para substituted benzoate ions shows that the great- “er mmberare approximately 32 or 33. Further Ostwala’” gives for the m-cyanobenzoievacid A 3 354. This is using however, a/\H':320 (18°C 2) giving a velue of 34 to the m-cyanobenzoate ion. It would seem logical to adopt 33 as the equivalent conductance of p-cyanobenzoate ion. The calculation of K, is therefore based on the value (347 + 33) = 380 tor/\pof p-cyanobenzoie acid. /\ H2347.(25°C) (10) Gstwald Zeit.Phy.Chem. 3, 241 (1889). (22) Ostwald Zeit.Phy.Chem. 3, 172 (1889). - Calculated Results. A: 380. Temp. 25 C. Number Concentration /. y -K&g x 10. 1 .007446 ON 70.8 186 31.6 2 -006936 73.0 192 31.7 3 .006909 72.8 2192 31.5 4 .004141 — 90.9 .239 31.1 5 .002059 119.6 2315 29.8 6 0008235 167.6 441 28.6 Average K, x 10 °=32.2. Even when a value of 50 is used for the p-cyanobenzo~ ate ion, or 377 ror/,, the value of K, x 10 is 31.5 or Ll ¢ higher. Terephthalamide, produced by the action of H,0, on p-cyanobenzoic acid~ proved tobe too insoluble to allow conductivity measurements to be made. Yet its K, can be determined by the hydrolysis of its sodium salt. Lack of time prevented making this determination. Conelusion. | This work was carried out under the direction of - Professor Howard J. Lucas. I am also indebted to - Dr. albert Raymond and Mr. Howard Winegarden for the use their conductivity apparatus; and to Dr. Stuart J. Bates for suggestions concerning the physical chemistry involved. (12) Kattwinkel and Yolffenstein B. 37, 3221 (1904) SUMMARY . Para cyanobenzoic acid was prepared by the Sandmeyer yeaction , as modified by Barl D. Stewart and its ioniza- tion constant determined by conductivity methods. The constant was found to be 31.2 x 10°. ( The meta acid has a value of 19.9 x 10°.) The solubility of p-cyanobenzoic acid is about .12 gm. in 100 cc. water at 20°C. -S The Ky, value of 51.2 x10 places the CN radical below the NO? radical in the p-substituted benzoic acids.