MAOS of D-gluconic acid, D-glucono-1,4- and 1,5-lactones, esters, hydrazides, and benzimidazoles thereof

Article abstract of DOI:10.1080/07328300701540258

Microwave-assisted organic synthesis (MAOS) of D-gluconic acid can be efficiently done by oxidation of D-glucose with bromine water, upon irradiation with microwave (MW). It was also used for the conversion of D-gluconic acid to ethyl D-gluconate, D-glucono-1,4- and 1,5-lactones, gluconyl hydrazide, and gluconyl phenylhydrazide in yields comparable to those obtained by conventional methods, but in much shorter times. A convenient microwave-mediated condensation of D-gluconic acid with o-phenylenediamines provided the respective acyclonucleoside benzimidazole in short time and good yield.

Full text of DOI:10.1080/07328300701540258

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MAOS of D‐Gluconic Acid, D‐Glucono‐1,4‐
and 1,5‐Lactones, Esters, Hydrazides, and
Benzimidazoles Thereof
E. S. H. El Ashry a , L. F. Awad a , H. Abdel Hamid a & A. I. Atta a
a Faculty of Science, Chemistry Department , Alexandria University ,
Alexandria, Egypt
b A. I. Atta is on leave from Faculty of Medical Sciences , Al‐Hodiedah
University , Yemen
Published online: 31 Aug 2007.
To cite this article: E. S. H. El Ashry , L. F. Awad , H. Abdel Hamid & A. I. Atta (2007) MAOS of D‐Gluconic
Acid, D‐Glucono‐1,4‐ and 1,5‐Lactones, Esters, Hydrazides, and Benzimidazoles Thereof , Journal of
Carbohydrate Chemistry, 26:5-6, 329-338, DOI: 10.1080/07328300701540258
To link to this article: http://dx.doi.org/10.1080/07328300701540258
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Journal of Carbohydrate Chemistry, 26:329–338, 2007
Copyright # Taylor & Francis Group, LLC
ISSN: 0732-8303 print 1532-2327 online
DOI: 10.1080/07328300701540258
MAOS of D-Gluconic Acid,
D-Glucono-1,4- and 1,5-
Lactones, Esters,
Hydrazides, and
Benzimidazoles Thereof
E. S. H. El Ashry, L. F. Awad, H. Abdel Hamid, and A. I. Atta
Faculty of Science, Chemistry Department, Alexandria University, Alexandria, Egypt
Microwave-assisted organic synthesis (MAOS) of D-gluconic acid can be efficiently done
by oxidation of D-glucose with bromine water, upon irradiation with microwave (MW). It
was also used for the conversion of D-gluconic acid to ethyl D-gluconate, D-glucono-1,4-
and 1,5-lactones, gluconyl hydrazide, and gluconyl phenylhydrazide in yields
comparable to those obtained by conventional methods, but in much shorter times. A
convenient microwave-mediated condensation of D-gluconic acid with o-phenylenedia-
mines provided the respective acyclonucleoside benzimidazole in short time and good
yield.
Keywords Gluconic acid, Gluconolactones, Microwave irradiation, Acyclonucleo-
sides, C-Nucleosides, Benzimidazole, Hydrazide
Received November 25, 2006; accepted June 22, 2007.
A. I. Atta is on leave from Faculty of Medical Sciences, Al-Hodiedah University, Yemen.
Address correspondence to El Sayed H. El Ashry, Faculty of Science, Chemistry Depart-
ment, Alexandria University, Alexandria, Egypt. E-mail: eelashry60@hotmail.com
329

E. S. H. El Ashry et al.
330
INTRODUCTION
Carbohydrates have attracted much attention as renewable biomass.[1]
Their polyfunctional nature makes them suitable for various transformations
into biodegradable and thus environmentally friendly materials. D-Gluconic
acid has a wide range of applications; it is involved in a large number of industrial
applications,[2,3] including complexing agents, key intermediates for foodstuffs,
detergents, textiles, leathers, photographic materials, or pharmaceuticals.[4–6]
On one hand, production of gluconic acid has utilized chemical, electro-
chemical, and bioelectrochemical approaches.[6–12] On the other hand, bio-
chemical strategies to oxidize glucose into gluconic acid relied on enzymes
such as Aspergillus niger,[8] Penicillium sp.,[9] Zymomonas mobilis,[10] and
Gluconobacter oxydans, or cells.[11–12]
The use of microwave (MW) technology has been reported to cause a
dramatic decrease in reaction time and possibly enhance the regio- and stereo-
selectivities in organic reactions.[13] In line with our desire to develop green
chemistry protocols, we applied this technique to our synthetic goals,[14]
among which was the preparation of gluconic acid and derivatives.
RESULTS AND DISCUSSION
Oxidation of D-glucose (1) with bromine water is one of the oldest and best known
reactions in carbohydrate chemistry.[15] Interestingly, microwave irradiation of a
mixture of D-glucose, bromine water, calcium carbonate, and calcium chloride in a
closed Teflon vessel for 10 min gave D-gluconic acid (3) in 83% yield. The conven-
tional method required 24 hours to give a comparable yield.
Alternatively, we have obtained D-gluconic acid from calcium gluconate by
reaction with oxalic acid in water under microwave irradiation for 1 min,
instead of the 20 min required to get a comparable yield under conventional
heating.[16] Since crystallization of D-gluconic acid from complex mixtures is
difficult, it is often achieved through its salts or readily crystallizable hydra-
zides.[17–18] In line with this observation, D-gluconic acid was reacted with
hydrazine hydrate or phenylhydrazine in ethanol under MW irradiation for
0.5 to 1.0 min to give the respective hydrazides 7 (80%) and 8 (97%) in crystal-
line forms, whereas conventional heating required 15 min.
Microwave irradiation of 3 in absolute ethyl alcohol containing a
catalytic amount of concentrated hydrochloric acid for 1 min gave ethyl
D-gluconate (4) in a yield of 66%, far superior to that obtained by
conventional heating (25%).[16] Attempted esterification of 3 by methyl
alcohol under the same conditions gave D-glucono-1,4-lactone (5) in 45%
yield instead of the expected ester. Alternatively, 5 could be obtained in 64%
yield by irradiation of D-glucono-1,5-lactone (6) in acetic acid for 2 min,
whereas conventional heating required 2 h to give 6 in 46% yield.[19] On the

Microwave-Assisted Organic Synthesis
331
other hand, 6 was isolated in quantitative yield upon irradiation of 3 in dioxane
for 2 min.
D-Gluconic acid (3), the ester 4, and lactone 6 gave identical hydrazides 7 or
8 upon MW irradiation in the presence of hydrazine or phenyl hydrazine,
respectively, for 0.5 to 1.0 min. Furthermore, MW irradiation of hydrazide 7
and p-nitrobenzaldehyde in ethanol for 1.5 min gave hydrazone 9 in 90%
yield. The conventional synthesis required heating for 2 h to give 9 in a
75% yield. The presence of the E and Z isomers was apparent in the 1H
NMR spectrum of 9, with two singlets at d 8.03 and 8.44 ppm corresponding
to the HC55N group and two singlets at d 11.42 and 11.70 ppm corresponding
to 55NꢀNH, twice in a 4.2:0.8 ratio.
Acyclic polyhydroxyalkyl derivatives of benzimidazole have been
prepared by condensation of o-phenylenediamines with aldonic acids in 35%
to 50% yield after purification by ion-exchange chromatography.[20a] In the
present work, syntheses of benzimidazoles 10 and 11 by reaction of 3 with
o-phenylenediamine and dimethyl-o-phenylenediamine, respectively, have
been carried out under MW irradiation for 1.5 to 2.0 min. The condensation
products 10 and 11 were readily isolated by chromatography postacetylation
to give 12 (70%) and 13 (63%) and subsequent quantitative deacetylation.
The structures of acetylated benzimidazoles 12 and 13 were confirmed by
1
H NMR spectroscopy, which revealed H-10 at d 6.06 ppm (d, J1 ,2 ¼ 7.7 Hz)
0
0
and d 5.95 ppm (d, J1 ,2 ¼ 8.4 Hz), respectively. The 13C NMR spectrum of 12
showed C-10 at dC 67.3 ppm and C55N at dC 146.7 ppm. The latter was absent
in the DEPT spectrum.
0
0
In conclusion, MW irradiation has been successfully employed for the
oxidation of D-glucose to D-gluconic acid, a highly desirable industrial
intermediate.
Moreover, the technique was also used for converting 3 to esters and 1,4- as
well as 1,5-D-gluconolactones, characterized as their hydrazides. An
acetylation-deacetylation protocol was used for the isolation of 2-(D-gluco-
pentitol-1-yl)benzimidazole, likewise prepared by microwave irradiation, as an
acyclonucleoside analog.[21] The shorter reaction times and in some cases the
higher yields make the use of this technique a good approach for the clean syn-
thesis of compounds 1–13, thus fulfilling the requirement to develop a “green”
method for preparing these compounds, and possibly new analogs (Scheme 1).
EXPERIMENTAL
General Methods
Melting points were determined on a Mel-temp apparatus and are
1
uncorrected. H NMR and 13C NMR spectra were recorded on a Bruker DRX

E. S. H. El Ashry et al.
332
Scheme 1

Microwave-Assisted Organic Synthesis
333
500 MHz or a Bruker Avance 300 MHz spectrometer. The chemical shifts are
expressed on the d scale using Me4Si as a standard, and coupling-constant
1
values are given in Hz. The assignments of H NMR spectra were based on
chemical-shift correlation DQFCOSY spectra, while the assignment of 13C
NMR spectra were based on heteronuclear multiple quantum coherence
(HMQC) experiments. TLC was preformed on Merck Silica Gel 60F254; the
spots were visualized by charring in sulfuric acid and by UV light. Irradiation
was achieved using a domestic microwave oven EM-230 M (800-watt output
power). The irradiation was done, unless otherwise stated, in a closed Teflon
cylindrical vessel, which was placed at the center of a rotating plate inside
the oven. The vessel was supported by a frame for safety. The vessel has an
outside diameter 6.5 cm and a length of 6.0 cm, whereas the space inside
the vessel was 3.0 cm wide and 2.0 cm long. Moreover, 2.0 cm in the length
inside the vessel was used to screw the cover tightly. The oven was adjusted
on the defrost mode with the fixed output power. Microanalyses were
preformed in the Microanalysis Unit at the Faculty of Science, Cairo
University.
D-Gluconic Acid (3)
Method a: In the Teflon vessel, a mixture of D-glucose (0.50 g, 2.78 mmol),
calcium chloride (0.05 g, 0.45 mmol), calcium carbonate (0.14 g, 1.40 mmol),
and water (10 mL) was treated with bromine (0.5 mL). The closed vessel was
irradiated for 10 min. The mixture was allowed to cool and neutralized by
calcium carbonate. The filtrate was evaporated until dryness and the residue
was extracted with ethanol, which upon evaporation gave 3 as a syrup
(0.45 g, 83% yield).
Method b: A mixture of calcium gluconate (15.0 g, 35 mmol), oxalic acid
(4.06 g, 45 mmol), and water (2 mL) was placed in an Erlenmeyer flask. This
was irradiated for 1.0 min, cooled, and then treated with water (25 mL). The
calcium oxalate was removed by filtration and washed with water (5 mL),
and the filtrate was evaporated under reduced pressure to give 3 as a syrup
(12.5 g, 92% yield).
Ethyl D-Gluconate (4)
A solution of 3 (0.5 g, 2.6 mmol) in absolute ethanol (10 mL) and one drop of
concentrated HCl was placed in a closed Teflon vessel and irradiated for 1 min
and then cooled. The reaction mixture was triturated with ethanol and the
product was recrystallized from ethanol to give colorless crystals (0.38 g, 66%
yield); mp. 62–648C; lit.[16] mp. 62–638C.

E. S. H. El Ashry et al.
334
D-Glucono-1,4-lactone (5)
(a) A mixture of 3 (0.25 g, 1.28 mmole), methanol (10 mL), and one drop of
concentrated HCl in a closed Teflon vessel was irradiated by microwave for
1.0 min. On cooling the product was separated, which upon recrystallization
from ethanol gave colorless crystals (0.10 g, 45% yield); mp. 134–1358C;
lit.[19] mp 133–1358C. (b) A solution of D-glucono-1,5-lactone (6) (0.25 g,
1.40 mmol) in glacial acetic acid (10 mL) containing one drop of concentrated
HCl was placed in a closed Teflon vessel and irradiated for 2 min. The
product was washed with glacial acetic acid, ethanol, and ether, then dried to
give 5 as colorless crystals (0.16 g, 64% yield); mp. 131–1338C; lit.[19] mp.
133–1358C.
D-Glucono-1,5-lactone (6)
A dry syrup of 3 (1.0 g, 5.2 mmol) was dissolved in dioxane (10 mL) and
water (1 mL) and the solution was irradiated for 1.0 min. The reaction
mixture was diluted with dioxane (10 mL), irradiated for a further 1.0 min,
and cooled, and the solution was nucleated with a crystal of the 1,5-lactone.
The product was recrystallized from ethanol (0.83 g, 92% yield); mp. 150–
1528C; lit.[19] mp. 150–1528C.
D-Gluconic Acid Hydrazide (7)
A mixture of 3, 4, or D-glucono-1,5-lactone (1 mmol), and hydrazine hydrate
(0.5 mL) in ethanol (10 mL) was placed in a conical flask where a funnel was
placed on its top and then irradiated for 0.5 min. The product was recrystal-
lized from ethanol to give colorless crystals (80% to 85% yield); mp. 144–
1468C; lit.[19] mp. 142–1448C; with decomposition at 177–1798C; lit.[19] 1768C.
D-Gluconic Acid Phenylhydrazide (8)
It was prepared as above using phenylhydrazine to give colorless crystals
(86% to 97% yield); mp. 203–2058C; lit.[17] mp. 200–2028C.
D-Gluconyl p-Nitrobenzylidene Hydrazide (9)
A mixture of 7 (0.21 g, 1 mmol) and p-nitrobenzaldehyde (0.15 g, 1 mmol) in
ethanol (10 mL) was irradiated for 1.5 min. The product was recrystallized
from ethanol to give 9 as pale yellow crystals (0.27 g, 90% yield); mp.
201–2038C as a 4.2:0.80 mixture of E and Z isomers; 1H NMR (500 MHz,
DMSO-d6) dH: 3.35 (dd, 1H, J4 ,3 ¼ 10.0 Hz, J4 ,5 ¼ 5.4, H-40), 3.55 (dd, 1H,
0
0
0
0
J3 ,2 ¼ 2.3 Hz, J3 ,4 ¼ 10.0, H-30), 3.49–3.44 (under DMSO, 2H, H-50, H-500),
0
0
0
0
3.94 (dd, 1H, J2 ,1 ¼ 4.6, J2 ,3 ¼ 2.3, H-20), 4.18 (d, 1H, J1 ,2 ¼ 4.6, H-10),
major isomer 7.90 (d, 1.66H, J3,5 ¼ 9.2, H-2, H-6), 8.26 (d, 1.66, J3,5 ¼ 9.2,
0
0
0
0
0
0

Microwave-Assisted Organic Synthesis
335
H-3, H-5), 8.44 (s, 0.83, CH55N), 11.42 (s, 0.83, 55NꢀNH, D2O-exchangaeble),
minor isomer 7.90 (d, 0.34H, J3,5 ¼ 9.2, H-2, H-6), 8.03 (s, 0.17H, CH55N),
8.22 (d, 0.34H, J3,5 ¼ 9.2, H-3, H-5), 11.70 (s, 0.17H,55NꢀNH, D2O-exchangae-
ble); 13C NMR (CDCl3) major isomer d: 63.8 (C-60), 71.0 (C-20), 72.0 (C-30), 72.4
(C-40), 74.1 (C-50), 124.6, 128.4, 141.3, 145.5 (Ar-C), 148.3 (HC55N), 170.1 (CO),
minor isomer d: 63.8 (C-60), 70.0 (C-20), 71.6 (C-30), 72.3 (C-40), 73.4 (C-50), 124.5,
128.4, 141.0, 145.5 (Ar-C), 148.0 (HC55N), 174.5 (CO). Anal Calcd. for
C13H17N3O8 (343.10): C, 45.30; H, 4.83; N, 12.18. Found: C, 45.01; H, 5.01; N,
12.47.
2-(1,2,3,4,5-Penta-O-acetyl-D-gluco-pentitol-1-
yl)benzimidazole (12)
A mixture of D-gluconic acid (0.50 g, 2.6 mmol) and o-phenylenediamine
dihydrochloride (1.08 g, 6 mmol) in ethanol (0.1 mL) and water (2 mL) was
placed in a closed Teflon vessel and irradiated for 2 min. The dried mixture
was suspended in dry pyridine (7 mL), cooled, and then treated with acetic
anhydride (10 mL). It was left overnight at rt and then poured into ice water
with stirring. The product was extracted with chloroform, washed with
water, dried over sodium sulfate, and evaporated. The residue was precipitated
by addition of hexane and recrystallized from methanol to give 12 as colorless
crystals (0.87 g, 70% yield); mp. 84–868C. 1H NMR (300 MHz, DDCl3) dH: 1.88,
0
0
0
00
1.93, 1.95, 1.96, 2.00 (5s, 15H, 5 ꢀ CH3CO), 4.07 (dd, 1H, J5 ,4 ¼ 5.5, J5 ,5
¼12.4, H-50), 4.20 (dd, 1H, J5 ,4 ¼ 2.8, J5 ,5 ¼12.4, H-500), 5.05 (ddd, 1H,
00
0
00
0
J4 ,3 ¼ 7.8, J4 ,5 ¼ 5.5, J4 ,5 ¼ 2.8, H-40), 5.30 (dd, 1H, J3 ,2 ¼ 2.5, J3 ,4 ¼ 7.8,
0
0
0
0
0
00
0
0
0
0
H-30), 6.00 (dd, 1H, J1 ,2 ¼ 7.7, J3 ,2 ¼ 2.5, H-20), 6.06 (d, 1H, J2 ,1 ¼ 7.7,
H-10), 7.52, 7.10 (dd, 4H, Ar-H), 11.9 (s, 1H, NH), 13C NMR (CDCl3) d: 19.5,
19.5, 19.6, 19.7 (4 ꢀ CH3CO), 60.8 (C-50), 67.3 (C-10), 67.6 (C-30), 67.7 (C-40),
68.5 (C-20), 114.7, 122.2, 136.7 (Ar-C), 146.7 (HC55N), 168.5, 168.9, 169.1,
169.3, 169.7 (5 ꢀ CH3CO). Anal Calcd. for C22H26N2O10 (478.45): C, 55.02; H,
5.64; N, 5.73. Found: C, 55.32; H, 5.94; N, 5.95.
0
0
0
0
0
0
5,6-Dimethyl-2-(1,2,3,4,5-penta-O-acetyl-D-gluco-pentitol-
1-yl)benzimidazole (13)
This was obtained analogously to compound 12 from 3 (0.50 g, 2.6 mmol)
and dimethyl-o-phenylenediamine dihydrochloride (1.08 g, 6 mmol). The
product was purified using column chromatography to give 13 as colorless
crystals (0.83 g, 63% yield); mp. 116–1188C. 1H NMR (500 MHz, CDCl3) d:
1.94, 2.04, 2.07, 2.08, 2.09 (5s, 15H, 5 ꢀ CH3CO), 2.31 (s, 6H, 2 ꢀ CH3), 4.04
(dd, 1H, J5 ,4 ¼ 5.4, J5 ,5 ¼ 12.2, H-50), 4.24 (dd, 1H, J5 ,4 ¼ 3.1, J5 ,5 ¼ 12.2,
0
0
0
00
00
0
00
0
H-500), 5.13 (ddd, 1H, J4 ,3 ¼ 7.6, J4 ,5 ¼ 5.4, J4 ,5 ¼ 3.1, H-40), 5.32 (dd, 1H
0
0
0
0
0
00
J3 ,2 ¼ 2.3, J3 ,4 ¼ 7.6, H-30), 5.95 (d, 1H, J2 ,1 ¼ 8.4, H-10), 6.05 (dd,
0
0
0
0
0
0
1H J2 ,3 ¼ 2.3, J2 ,1 ¼ 8.4, H-20), 7.2–7.80 (2dd, 2H, Ar-H), 9.92 (s, 1H, NH,
0
0
0
0

E. S. H. El Ashry et al.
336
D2O-exchangeable). Anal Calcd. for C24H30N2O10 (506.19): C, 57.33; H, 6.45; N,
5.25. Found: C, 57.03; H, 6.14; N, 5.55.
2-(D-Gluco-pentitol-1-yl)benzimidazole (10)
A suspension of 12 (1 g, 2.09 mmol) in dry methanol (50 mL) was treated
with a solution of sodium methoxide (2 mL; prepared from 0.1 g sodium in
20 mL methanol). The reaction mixture was left overnight at rt and neutralized
with ion-exchange resin. The solution was filtered and concentrated under
reduced pressure to give a residue that was recrystallized from methanol to
give 10 as colorless crystals (0.49 g, 90% yield); mp. 220–2218C, lit.[15] mp.
215–2178C.
2-(D-Gluco-pentitol-1-yl)-5,6-dimethylbenzimidazole (11)
It was obtained, analogously to compound 10, from compound 13 (1 g,
1.97 mmol) colorless crystals (0.51 g, 90% yield); mp. 204–2058C. 1H NMR
0
0
(500 MHz, DMSO-d6) d: 2.24 (s, 6H, 2 ꢀ CH3), 3.25 (dd, 1H, J5 ,4 ¼ 7.6,
J5 ,5 ¼ 11.5, H-50), 3.30 (dd, 1H, J5 ,4 ¼ 5.4, J5 ,5 ¼ 11.5, H-500), 3.49 (ddd,
0
00
00
0
00
0
1H, J4 ,5 ¼ 6.1, J4 ,5 ¼ 5.4, H-40), 3.96 (d, 1H, J2 ,1 ¼ 6.1, H-20), 3.57 (under
0
0
0
00
0
0
DMSO, H-30), 4.83 (d, 1H, J2 ,1 ¼ 6.9, H-10), 7.27, 7.18 (2s, 2H, Ar-H), 11.99
(s, 1H, NH, D2O-exchangaeble). Anal Calcd. for C14H20N2O5 (296.32): C,
56.56; H, 6.68; N, 9.79. Found: C, 56.46; H, 6.36; N, 9.48.
0
0
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