Basicity Constants(pK ) of 5-Substituted 2-Furaldehydes 5- 2-Furaldehyde

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(1)Journal of the Korean Chemical Society 2002, Vol. 46, No. 4 Printed in the Republic of Korea. 2-Furaldehyde . 5-. *

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(4) (2002. 6. 4 ). ‡. †. ‡. Basicity Constants(pKBH+) of 5-Substituted 2-Furaldehydes Jong-Pal Lee*, Gui-Taek Lim, Yong-Hee Lee, In-Sun Koo†, and Zoon-Ha Ryu‡ Department of Chemistry, Dong-A University, Pusan 604-714, Korea † Department of Chemical Education, Gyeongsang National University, Chinju 660-701, Korea ‡ Department of Chemistry, Dongeui University, Pusan 614-714, Korea (Received June 4, 2002). . 5- 2-furaldehyde 25 C, !"# $%%&'() *+, - ./ 01& 2 pK 3 &(excess acidity) '() 4+56. 78 19 :; 5-methyl-2furaldehyde 01& < =8 19 :; 5-nitro-2-furaldehyde 01& >6 ?8 @AB(C pK DE) 3.25 F& GH: @< I J KL6. - 1/ () M NO P Q F& 9 @AR< m*3S T UV WX ./2 acetophenone YZX ?1) @A[ J KL6. 2furaldehyde 1 \ " ]^ 01& \ 32 −∆pK m* __U: `S ab >56. : &', 01& , 5- 2-furaldehyde, $%%&' o. BH+. BH+. ABSTRACT. The protonation equilibrium of 5-substituted 2-furaldehydes is investigated spectrophotometrically in aqueous sulfuric acid at 25 oC and the basicity constants(pKBH+) of the substrates is calculated by means of the excess acidity method. The basicity constant of 5-metyl-2-furaldehyde having electron donating group is larger than that of 5nitro-2-furaldehyde having electron withdrawing group. Difference between the basicity constants(pKBH+) of these two compounds was about 3.25 pK unit. The m* value which is the degree of solvation of the protonated substrate is similar to that of acetophenone having same protonation site. The dependence of pKBH+ on m* value shows good linear correlation. Keywords:. Excess Acidity Method, Basicity Constant, 5-Substituted-2-Furaldehyde. c1 !"# defgh i. jh k FS Hl i. WX Um nopq " X F>9 r1 Ej sS _t H uv w 6. 1926x Hammett< 25 C . !"# y* n A z {| y* jh) M rS }) 1. o. M ~ +, 4*V __U9 *+< f X 9 L6. H" j, )gh i." X 4*V _ _U 9 ~() @A }< 6. Spinelli S )gh9 j# u< 1 " X ~ *+g : phenylthiophen-2-ylmethanone (pro2. 3. 323.

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(6) . 324. tonation) *+,, Hl i.l P" X H 3 pK 3 $%%&'() &'(excess acidity method)" j U X :K 6. @ Spinelli phenylthiophen-2-ylmethanone" X S o>1 " defghV def )gh " 1 9 \ 1 " X 456. Lee S def )gh 1 9 *+1 E+, "# >< V H 5 ) gh ) ¡9 Y=NH(pyrrole), Y=O(furan) Y= PH(phosphole) hg Y=S(thiophene)() ¢L 2£ 5£ E ¤¥¡ + z "¦ Y= ) ¡ Z=1 \ : v§8 \ u<:9 H¨© () *X K6. BH+. 4. S Aldrich ®¯ ) +5 6. *" X °< 3G °" ± K< CO gas9 +1 Ej N gas9 bubbling ² +5(C, *" X ³´ ³FS Katayama 0.1 N NaOH() F µX ¶&9 ·F+56. b¸X 1/ ¹º»¼ r< X 11 < Shimadzu TB-85N ½*" ·X Hewlett Packard 8452A Diode Array Spectrophotometer9 +56..

(7) . 01(B) P" X H. 32 pK ·FS &¾(excess acidity function: EA) '( 2) H+, 4+56. (2)"# 2-furaldehyde. 2. 2. BH+. logI − logCH+ = pKBH+ + m*X. (2). F ¶&"# 01V 01" X P ¶&Y pK : 01 B P H 3 m*: P-01 ¿(conjugate acid-base pair) ©2 Q F& X(&): _kO &V À &V GH9 @A6. Á, I < F ¶&"# 01 B H Y I = C----------H6. C ,1"# C V C < 01 BV P BH ¶&: O6. F ¶&"# Hl -- ¶&< (3)"# @A V H 01 BV P BH u< Â %& Y) ·F K6. I:. BH+. T 4< ª~©() a 4 >gO : < def 5 )gh i.2 2-furaldehyde(1-a), 5methyl-2-furaldehyde(1-b), 5-bromo-2-furaldehyde(1-c). hg 5-nitro-2-furaldehyde(1-d) !"# $%%&'() *+, Hl. i. P jh 32 pK 3 Cox " W&O &'(excess acidity method)" j 4 +g H9 «() - 1" X 1 3 4+g T ª~ ¬+56.. 5. BH+. +. BH B. +. B. BH+. +. D – DB C BH+ I = ----------= -------------------+ D CB BH – D (1). (3). (3)"# D: F ¶&"# 1/ :+Ã kFX Â %& D : 01 Â%& D : ;X "# 01 Â%& 0 1 P" X Â%&9 @A6. EA'" X 5-bromo-2-furaldehyde pK ·F d' Ä9 lÅ ÆbF¶& "# 5bromo-2-furaldehyde" O F&2 H Y I= B. . 1/2 2-furaldehyde, 5-methyl2-furaldehyde, 5-bromo-2-furaldehyde hg 5-nitro-. BH+. BH+. Journal of the Korean Chemical Society.

(8) 2-Furaldehyde . 325. 5-. Table 1. Maximum absorption wavelength for base B and the corresponding protonated form BH+ of 5-substituted-2-furaldehydes(5-X-FA) 5-X-FA X. Fig. 1. UV spectrum of 5-bromo-2-furaldehyde in water.. CH3 H Br NO2. B. BH+. λmax. λmax. 294 278 292 310. 326 308 340 320. Â {Ç Table 1" @ARL6. 5-bromo-2-furaldehyde(1-c) pK 3 ·F+1 E+, ¶&9 52.5 w/w%"# 74.0 w/ w%) \ rS Â%&) M excess acidity function" u< - ½ 3 ·F+, Table 2" É+56. H }9 H+, excess acidity X" u< logI-logC 3 plot+, ¡ÊË ÌÇX ÍÎ() M 5-bromo-2-furaldehyde(1-c) pK 3 4+56. H :ÈX excess acidity ÏÐ"# logI-logC 3 plot+, Fig. 3" @ARL 6. ¡ÊË ÌÇX ÍÎ3, (1-c) pK 3H -3.15: Ñ J KL6. ÃÒ:) 2-furaldehyde (1-a), 5-methyl-2-furaldehyde(1-b) hg, 5-nitro-2-furaldehyde (1-d)" X pK 3 ·F&(1-c) pK 3 ·F d' Ó+8 excess acidity function ÍÎ() M 4+56. - 1/(1-a), (1-b) hg (1-d) $% © }V H9 X } $Ô() M rS Õ³9 Table 3-5, hg Fig. 4-6" @ARL6. BH+. Fig. 2. Absorption spectra for protonation of 5-bromo-2-furaldehyde in the range of 70.0 w/w%~94.0 w/w% aqueous sulfuric acid solution.. H+. BH+. 9 ·F+1 E+, Æb 012 5-bromo-2furaldehyde(B)V 01 N2 O 5-bromo2-furaldehyde(BH ) Â {Ç 25 C"# kF X6. H X Q< -- . 88.0 w/w% (kF :ÈX ;X ) !"# kF+ 56. kFO Â {ÇS Fig. 1, Fig. 2"# >< V H _kO ¹º»¼() M . !"# 292 nm, !"# 340 nm) F+56. HV S d '() - 1/" X 01N N" X CBH+/CB. +. o. H+. BH+. BH+. BH+. Table 2. Values of excess acidity function and ionization ratio of 5-bromo-2-furaldehyde in 52.5 w/w%~74.0 w/w% aqueous sulfuric acid at 25 oC. w/w% acid. logCH+a). Xa). D340. 52.5 55.0 57.5 60.0 62.5 65.0 67.5 70.0 72.0 74.0. 0.970 0.992 1.014 1.033 1.052 1.069 1.084 1.097 1.108 1.118. 2.548 2.763 2.992 3.238 3.505 3.795 4.112 4.459 4.759 5.080. 0.221 0.246 0.376 0.376 0.497 0.608 0.673 0.852 1.059 1.296. Dmax=1.983, DB=0.0724, λmax=340 nm a). taken from reference 5.. 2002, Vol. 46, No. 4. logI. logI/CH+. −1.074 −1.000 −0.724 −0.724 −0.544 −0.409 −0.339 −0.162 0.028 0.251. −2.044 −1.992 −1.737 −1.757 −1.596 −1.478 −1.423 −1.259 −1.080 −0.867.

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(10) . 326. 3 Table 6" @ARL6. m*3S 01 × K Ø p| P-P01¿(conjugate acidbase pair) ©2 Q F&" X F>9

(11) j ´6. T ª~"# UO m*3S Table 6"# > < V H 0.39"# 0.66 3 :Ù J K6. m*3H YZ+Å QV / ÚÛH YZ+8 Óv[ Ü+Ý) /2 2-furaldehydeV Q2 Q < b¸X 1/ 1: \j & ?8 GH: @ Þß j 7g K6. XÎ 1: \¾" ]| 01& (pK ) \. : m*3 vàX _ _U9 >H<:9 *+1 E+, Fig. 7 H -∆pK " X - 1/ m*3 &+56. “ß” 1á19 â< `S ab _U: @A[ > excess acidity '() 4X 1/ 01& (pK )< ãÁ AãH K < 3() }O6. m*3 : i."# rv; 3 Yj >Å Spinelli: 4 >gX phenylthiophen-2-ylmethanone 6-8. BH+. Fig. 3. Plot of (logI-logCH+) vs. excess acidity, X for 5-bromo2-furaldehyde in aqueous sulfuric acid at 25 oC.. . BH+. BH+. ./ (1-a), (1-b), (1-c) hg (1-d) . "# ÖN 3 Ð2 pK 3 m* BH+. Table 3. Values of excess acidity function and ionization ratio of 2-furaldehyde in 52.5 w/w%~72.0 w/w% aqueous sulfuric acid at 25 oC w/w% acid. logCH+. X. D308. logI. logI/CH+. 52.5 55.0 57.5 60.0 62.5 65.0 67.5 70.0 72.0. 0.970 0.992 1.014 1.033 1.052 1.069 1.084 1.097 1.108. 2.548 2.763 2.992 3.238 3.505 3.795 4.112 4.459 4.759. 0.419 0.501 0.563 0.689 0.758 0.942 1.009 1.364 1.544. −0.873 −0.741 −0.657 −0.512 −0.443 −0.279 −0.224 0.049 0.187. −1.844 −1.733 −1.671 −1.545 −1.495 −1.348 −1.308 −1.048 −0.921. Dmax=2.452, DB=0.147, λmax=308 nm Table 4. Values of excess acidity function and ionization ratio of 5-methyl-2-furaldehyde in 15.0 w/w%~55.0 w/w% aqueous sulfuric acid at 25 oC w/w% acid. logCH+. X. D326. logI. logI/CH+. 15.0 20.0 30.0 35.0 40.0 45.0 50.0 52.5 55.0. 0.315 0.461 0.674 0.757 0.828 0.891 0.945 0.970 0.992. 0.387 0.573 1.038 1.317 1.628 1.969 2.345 2.548 2.763. 0.155 0.174 0.227 0.255 0.318 0.432 0.586 0.717 0.831. −2.030 −1.771 −1.405 −1.286 −1.095 −0.866 −0.654 −0.516 −0.412. −2.348 −2.229 −2.078 −2.043 −1.923 −1.757 −1.599 −1.486 −1.404. Dmax=2.634, DB=0.132, λmax=326 nm Journal of the Korean Chemical Society.

(12) 2-Furaldehyde . 327. 5-. Table 5. Values of excess acidity function and ionization ratio of 5-nitro-2-furaldehyde in 82.0w/w%~92.0w/w% aqueous sulfuric acid at 25 oC w/w% acid 82.0 86.0 88.0 90.0 92.0. logCH+ 1.143 1.109 1.066 0.996 0.894. X 6.528 7.277 7.637 7.985 8.340. D320 1.181 1.475 1.571 1.686 1.714. logI -0.334 0.181 0.336 0.573 0.576. logI/CH+ -1.477 -0.929 -0.730 -0.423 -0.318. Dmax = 1.840, DB = 0.876, max = 320nm. Fig. 4. Plot of (logI-logCH+) vs. excess acidity, X for 2-furaldehyde in aqueous sulfuric acid at 25 oC.. Fig. 6. Plot of (logI-logCH+) vs. excess acidity, X for 5-nitro2-furaldehyde in aqueous sulfuric acid at 25 oC. Table 6. Acid dissociation constants, pKBH+ and m* values for 5-X-2-furaldehyde(5-X-FA) in aqueous sulfuric acid at 25 oC 5-X-FA. X CH3 H Br NO2. pKBH+. m*. ∆pKBH+. −2.50 −2.87 −3.15 −5.75. 0.39 0.40 0.44 0.66. −0.37− 0.00 0.28 2.88. ∆pKBH+=(pKBH+)H−(pKBH+)X. H 2-furaldehydeV YZX m*3 â< ./lS acetophenone V benzamide À J Kg, benzoate "#< m*3H ¯ç ?8 @A[ J K6. XÎ - ./l pK 3S Table 6"# >< V H 2-furaldehydes 5£ E" K< 1: 78 1"# =8 1) \ 3.25 pK F& ÛÙ è K6. HV S eS 2furaldehyde 5£ E" 78 19 :; Æ, =8 19 :; Æ >6 o> ¤¥ " : éê ë8 Óvì IHÝ) 01& 6. Fig. 5. Plot of (logI-logCH+) vs. excess acidity, X for 5-methyl2-furaldehyde in aqueous sulfuric acid at 25 oC.. 3 kF"# UO m*3S Öä3() 0.97å 0.03H O6g +56. HV S ·< phenylthiophen2-ylmethanoneV Q ÚÛH 2-furaldehyde V Q ÚÛ>6 ?8 Óv[()# phenylthiophen- 2-ylmethanone P Q : 1 / F æ< : 2-furaldehyde >6< ? 6< ª j 7g K6. Table 7"# >< V. pKBH+. 2002, Vol. 46, No. 4. 9. 10. BH+.

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(14) . 328. "# 5--2-furaldehyde " X P jh(pK )9 4+, 6ß S ·¨ rL6. 1. 2-furaldehyde 01& < 5£ E 1 : 78 1 ÓÉ ?8 @AB(C m*3S Û 8 @Aõ6. H< 78 1 ÓÉ P(BH ) ë8 lv Q : ö Óv[ J KL6. 2. T ª~"# 4X m*3S 0.39~0.66 H 3 >56. H< T 1/ WX acetophenone m*3(0.50~0.60) YZ+8 _ku< I > Q. F&: YZ+8 Óv[ J KL6. 3. Hammett dF 1 3" jã+< -∆pK 3S Hammett 1 3 YZX eH Kß J KL6. 4. m*3" X -∆pK ÷&< 7 `S ab _U: øÑ J KL6. BH+. +. Fig. 7. Basicity dependence on m* for 5-substituted-2-furaldehydes. Table 7. Comparison of m* value for furaldehydes with those of typical aromatic acyl derivatives Compounds 2-Furaldehydes Acetophenones Benzamides Methylbenzoate Eethylbenzoate. m* 0.39~0.66 0.50~0.60*) 0.54*) 0.81*) 0.73*). BH+. *): taken from ref. 11). 2 pK : =8 19 :; Æ >6 í 3 :/ IH6. T ª~"# rS ·< HX Äk Ó +< ·À() > AãH K6g }O6. )gh i. 4" j "¦ ab _U9 ©X 4 >g: K6. Hl" +Å X î ) ¡9 :< 5 )gh. i."# 5£ E" 1< yïgh" 1: : < i. Yð para E) ç7 K (Ý) HX i. 4*V __U9 HammettN dF() _ñò K6g +56. T 4"# b¸X 1/H 5--2-furaldehyde HÝ) 4X pK 3() M Hammett dF"# 1 2 σ3 6ß (4)() M 4 K IH6. BH+. 12. 12. BH+. -∆pKBH+ = (pKBH+)5-X − (pKBH+)5-H. (4). (4)() M UO -∆pK 3S Table 6"# : UX 1 3 WX e2 78 12 Æ< “-”3, =8 12 Æ “+”3 @ARg Kß 7ó ·|g ô-X6. BH+. Hammett. BH+. H ùúS 2001x& û4Y(üÌ D14{ý) ¡"+, 4uL(C, H" þ ÿøp6.. 1. Kresge, A. J.; Chen, H. L.; Chiang, Y.; Murrill, E.; Payne, M. A.; Sagatys, D. S. J. Am. Chem. Soc. 1971 93, 413. 2. Hammett, L. P. Physical Organic Chemistry, McGrawHill, New York, 2nd Ed. 1970. 3. Noto, R.; Gruhadauria, M.; Rosselli, S.; Spinelli, D. J. Chem. Soc., Perkin Trans. 2, 1996, p. 829. 4. Lee, I.; Rhee, S. K.; Kim, C. K.; Chung, D. S.; Kim, C. K. Bull. Korean Chem. Soc. 2000, 21(9), 882. 5. Cox, R. A.; Yates, K. J. Am. Chem. Soc. 1978, 100, 3862. 6. Chimichi, S.; Dell’Erba, C.; Gruttadanria, M.; Noto, R.; Novi, M.; Petillo, G.; Sancassan, F.; Spinelli, D. J. Chem. Soc., Perkin Trans. 2. 1995, 2, 1021. 7. Cox, R. A.; Yates, K. J. Am. Chem. Soc. 1978, 100, 3861. 8. Bagno, R.; Scorrano, G.; More OFerall, R. A. Rev. Chem. Intermed., 1987, 7, 313. 9. Yates, K.; Wai, H.; Welch, G.; Meclelland, R. A. J. Am. Chem. Soc. 1973, 9, 418. Journal of the Korean Chemical Society.

(15) 2-Furaldehyde . 5-. 10. R. A. Cox, R. A.; Tates, K. Can, J. Chem. 1979, 57. 2944-2951. 11. (a) Cox, R. A.; Smith, C. R.; Yates, K. Can. J. Chem. 1979, 57, 2952; Cox, R. A.; Yates, K. J. Org. Chem. 1986, 51, 3619; (b) Levi, A.; Modena. G.; Scorrano, G. J. Am. Chem. Soc. 1974, 96, 6585: (c) Azzaro, M.; Gal, J. F.; Geribaldi, S.; Grec-Luciano, A.; Catteri, C. J. Chem. Res. (s), 1979, 134; (d) Stewart, R.; Yates, K. J. Am. Chem. Soc. 1958, 80, 6355; (e) Dahn, H.; Pechy, P.; Toan, V. V. Angew. Chem., Int. Ed. Engl., 1990, 29, 647; (f) Brownlee, R. T. C.; Sadek, M.; Craik, D. J.. 2002, Vol. 46, No. 4. 329. Org. Magn. Reson., 1983, 21, 616: (g) Gilbert, T. J.; Johnson, C. D. J. Am. Chem. Soc., 1974, 96, 5846; (h) Dell’Erba, C.; Mele, A.; Novi, M.; Petrillo, G.; F. Sancassan, F.; Spinelli, D.; J. Chem. Soc., Perkin Trans. 2. 1990, 2055; (i) Dell’Erba, C.; Sancassan, F.; Novi, M.; Petrillo, G.; Mugnoli, A.; Spinelli, D.; Consiglio, G.; Gatti, P. J. Org. Chem., 1988, 53, 3564. 12. Jaffe, H. H.; Jones, H. L. Advance in Heterocyclic Chemistry, Academic Press, New York, 1964, 3, 209; Tomasik, P.; Tohnson, C. D. Ibid. 1976, 20, 1..

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Basicity Constants(pK ) of 5-Substituted 2-Furaldehydes 5- 2-Furaldehyde  

Basicity Constants(pK ) of 5-Substituted 2-Furaldehydes 5- 2-Furaldehyde