Theoretical Study on the Selective Redox Mechanism of Benzaldehyde in Photo-catalyzed Reaction†

doi:10.7503/cjcu20150719

Abstract

Abstract:

The photoelectron and photohole could be generated on the surface of TiO₂ under the UV irradiation. Some reactive species could be produced indirectly. The photoelectron could be trapped by oxygen leading to yield the superoxide anion radicals, while the photohole can react with the solvent molecules to generate the hydroxyl radical and alcohol radical. The substrate may be reduced by the photoelectron directly, or by alcohol radicals. And it may be oxidized by the photohole directly, or by the reactive species of hydroxyl radicals and superoxide anion radicals. The M06-2X/6-311G^* method was employed to investigate the selective redox mechanism of benzaldehyde in solution, which was reduced or oxidized by the reactive species generated during the photo-catalyzed process in different reaction conditions. According to the computation results, the photo-redox reaction of benzaldehyde would be happened in room temperature. In oxygen-free ethanol solvent, the ethanol molecules could react with the oxidizing species to yield the alcohol radicals, while benzaldehyde could be mainly reduced to benzyl alcohol. In oxygen-rich without ethanol condition, the reductive photoelectron is trapped by oxygen to prohibit the reduction of benzaldehyde, so benzaldehyde is mainly oxidized to benzoic acid.

Key words: Benzaldehyde, Photocatalysis, Mechanism of selective redox reaction, Density functional theory

CLC Number:

O644.14

TrendMD:

HUANG Xiao, GAN Hanlin, PENG Liang, GU Fenglong. Theoretical Study on the Selective Redox Mechanism of Benzaldehyde in Photo-catalyzed Reaction^†[J]. Chem. J. Chinese Universities, 2016, 37(2): 297.

Figures/Tables 12

Scheme 1 Possible reaction mechanism of benzaldehyde being reduced to benzyl alcohol photo-catalyzed by TiO2

Fig.1 Gibbs free energy profile for the reactions between ·OH and ethanol replete with optimized structures Bond distances are in nm.

Fig.2 Gibbs free energy profile for the reactions between C2H5O· or ·CH2CH2OH and ethanol replete with optimized structures Bond distances are in nm.

Fig.3 Gibbs free energy profile for the process from BHA to ·CO(Ph) replete with optimized structures Bond distances are in nm.

Scheme 2 Possible reaction mechanism of BHA being reduced to BA in ethanol The solid lines represent the dominant pathways.

Fig.4 Gibbs free energy profile for the process from BHA to IM2 replete with optimized structures Bond distances are in nm.

Fig.5 Gibbs free energy profile for the process from IM2 to BA replete with optimized structures Bond distances are in nm.

Scheme 3 Possible reaction mechanism of BHA being oxidized to BAC in water The solid lines represent the dominant pathways.

Fig.6 Gibbs free energy profile for the process from BHA to IM4 replete with optimized structures Bond distances are in nm.

Fig.7 Gibbs free energy profile for the process from BHA to IM5 replete with optimized structures Bond distances are in nm.

Table 1 Relative Gibbs free energies for the processes from IM4 and IM5 to BAC

Species	G/a.u.	ΔG/a.u.	ΔG/(kJ·mol^-1)	Species	G/a.u.	ΔG/a.u.	ΔG/(kJ·mol^-1)
IM4+^·OH	-496.905943	0	0	IM5+^·OH	-420.519329	0	0
BAC+H₂O	-497.083805	-0.177862	-466.98	BAC	-420.680582	-0.161253	-423.37

Table 2 Relative Gibbs free energies for the processes from O2 and BHA to O2·- and IM1 in different solvents

Species	G/a.u.	ΔG/a.u.	ΔG/(kJ·mol^-1)	Species	G/a.u.	ΔG/a.u.	ΔG/(kJ·mol^-1)
O₂(in ethanol)	-150.321004	0	0	BHA(in ethanol)	-345.433966	0	0
$O 2 · -$ (in ethanol)	-150.439021	-0.118017	-309.85	IM1(in ethanol)	-345.522669	-0.088703	-232.89
O₂(in water)	-150.320706	0	0	BHA(in water)	-345.429490	0	0
$O 2 · -$ (in water)	-150.447154	-0.126448	-331.99	IM1(in water)	-345.522900	-0.093410	-245.25

Table 2 Relative Gibbs free energies for the processes from O2 and BHA to O2·- and IM1 in different solvents

Species	G/a.u.	ΔG/a.u.	ΔG/(kJ·mol^-1)	Species	G/a.u.	ΔG/a.u.	ΔG/(kJ·mol^-1)
O₂(in ethanol)	-150.321004	0	0	BHA(in ethanol)	-345.433966	0	0
$O 2 · -$ (in ethanol)	-150.439021	-0.118017	-309.85	IM1(in ethanol)	-345.522669	-0.088703	-232.89
O₂(in water)	-150.320706	0	0	BHA(in water)	-345.429490	0	0
$O 2 · -$ (in water)	-150.447154	-0.126448	-331.99	IM1(in water)	-345.522900	-0.093410	-245.25

References 30

[1]	Hoffmann M. R., Martin S. T., Choi W., Bahnemann D. W., Chem. Rev., 1995, 95(1), 69—96
[2]	Hagfeldt A., Grätzel M., Acc. Chem. Res., 2000, 33(5), 269—277
[3]	Nowotny J., Sorrell C. C., Bak T., Sheppard L. R., Sol. Energy, 2005, 78(5), 593—602
[4]	Chong M. N., Jin B., Chow C. W. K., Saint C., Water Res., 2010, 44(10), 2997—3027
[5]	Joyce-Pruden C., Pross J. K., Li Y. Z., J. Org. Chem., 1992, 57(19), 5087—5091
[6]	Park H., Choi W., Catal. Today, 2005, 101(3/4), 291—297
[7]	Zhang M., Wang Q., Chen C. C., Zang L., Ma W. H., Zhao J. C., Angew. Chem. Int. Ed., 2009, 48(33), 6081—6084
[8]	Ferry J. L., Glaze W. H., Langmuir, 1998, 14(13), 3551—3555
[9]	Wu W. M., Wen L. R., Shen L. J., Liang R. W., Yuan R. S., Wu L., Appl. Catal. B, 2013, 130—131, 163—167
[10]	Mills A., O’Rourke C., J. Photochem. Photobiol. A, 2012, 233, 34—39
[11]	Su F. Z., Mathew S. C., Lipner G., Fu X. Z., Antonietti M., Blechert S., Wang X. C., J. Am. Chem. Soc., 2010, 132(46), 16299—16301
[12]	Wang D. B., Zhao L. X., Guo L. H., Zhang H., Wan B., Yang Y., Acta Chim. Sinica, 2015, 73(5), 388—394
	(王大彬, 赵利霞, 郭良宏, 张辉, 万斌, 杨郁. 化学学报, 2015, 73(5), 388—394)
[13]	Xu Y. M., Prog. Chem., 2009, 21(2), 524—533
	(许宜铭. 化学进展, 2009, 21(2), 524—533)
[14]	He H. Y., Zapol P., Curtiss L. A., Energy Environ. Sci., 2012, 5(3), 6196—6205
[15]	Huang X., Peng L., Li S. P., Gu F. L., Theor. Chem. Acc., 2015, 134(2), 3-1—12
[16]	Huang X., Peng L., Gu F. L., Zhang R. Q., Phys. Chem. Chem. Phys., 2015, 17(30), 19997—20005
[17]	Kılıç M., Koçtürk G., San N., Çınar Z., Chemosphere, 2007, 69(9), 1396—1408
[18]	Shen Y. L., Hao J. K., Cao Y. Y. , Yang Y. C., Chem. J. Chinese Universities, 2007, 28(9), 1743—1746
	(申勇立, 郝金库, 曹映玉, 杨恩翠. 高等学校化学学报, 2007, 28(9), 1743—1746)
[19]	Wang S., Wang W. N., Gao Z. F., Wang W. L., Chem. J. Chinese Universities, 2015, 36(8), 1588—1595
	(王帅, 王渭娜, 高志芳, 王文亮. 高等学校化学学报, 2015, 36(8), 1588—1595)
[20]	Zhao Y., Truhlar D. G., Theor. Chem. Acc., 2008, 120(1—3), 215—241
[21]	Fukui K., Acc. Chem. Res., 1981, 14(12), 363—368
[22]	Marenich A. V., Cramer C. J., Truhlar D. G., J. Phys. Chem. B, 2009, 113(18), 6378—6396
[23]	Legault C.Y., CYL View Version 1.0b, University of Sherbrooke, Sherbrooke, 2009
[24]	Frisch M.J., Trucks G. W., Schlegel H. B., Scuseria G. E., Robb M. A., Cheeseman J. R., Scalmani G., Barone V., Mennucci B., Petersson G. A., Nakatsuji H., Caricato M., Li X., Hratchian H. P., Izmaylov A. F., Bloino J., Zheng G., Sonnenberg J. L., Hada M., Ehara M., Toyota K., Fukuda R., Hasegawa J., Ishida M., Nakajima T., Honda Y., Kitao O., Nakai H., Vreven T., Montgomery J. A., Peralta J. E., Ogliaro F., Bearpark M., Heyd J. J., Brothers E., Kudin K. N., Staroverov V. N., Keith T., Kobayashi R., Normand J., Raghavachari K., Rendell A., Burant J. C., Iyengar S. S., Tomasi J., Cossi M., Rega N., Millam J. M., Klene M., Knox J. E., Cross J. B., Bakken V., Adamo C., Jaramillo J., Gomperts R., Stratmann R. E., Yazyev O., Austin A. J., Cammi R., Pomelli C., Ochterski J. W., Martin R. L., Morokuma K., Zakrzewski V. G., Voth G. A., Salvador P., Dannenberg J. J., Dapprich S., Daniels A. D., Farkas O., Foresman J. B., Ortiz J. V., Cioslowski J., Fox D. J., Gaussian 09, Revision C. 01, Gaussian Inc., Wallingford CT, 2010
[25]	Jaeger C. D., Bard A. J., J. Phys. Chem., 1979, 83(24), 3146—3152
[26]	Dmitrenko O., Thorpe C., Bach R. D., J. Org. Chem., 2007, 72(22), 8298—8307
[27]	Boronat M., Viruela P., Corma A., J. Phys. Chem. B, 1997, 101(48), 10069—10074
[28]	Legrini O., Oliveros E., Braun A. M., Chem. Rev., 1993, 93(2), 671—698
[29]	Bahnemann W., Muneer M., Haque M. M., Catal. Today, 2007, 124(3/4), 133—148
[30]	Luo Y. L., Liu Y. J., Chem. J. Chinese Universities, 2015, 36(1), 24—33
	(罗艳玲, 刘亚军. 高等学校化学学报, 2015, 36(1), 24—33)