2-Hydroxy-1-methylethyl benzoate (16):22 1H NMR (CDCl3,
250 MHz) δ 1.27 (m, 3H), 3.76 (d, 2H), 5.21 (m, 1H), 7.42-7.56
1,3-propanediol (3) was also monobenzoylated with a
high selectivity, but the yield was less than those
involving ethylene glycol (entries 1 and 11). Benzalde-
hyde can also be converted to the corresponding glycol
monoester 15 when treated with diethylene glycol (4).
This reaction constitutes the first satisfactory method for
the direct synthesis of diethylene glycol monobenzoate
15 (entry 12). Glycol monoesters such as those of ethylene
glycol have been used as cross-linking agents for poly-
esters or as fungicides. The present method indirectly
provides a useful means for the selective monoprotection
of some diols. We believe that this constitutes the first
satisfactory method for the direct conversion of aldehydes
to the corresponding glycol monoesters. Exhaustive CAS
searches have led us to this conclusion.
This method is useful for the selective monoprotection
of unsymmetrical glycols when in fact a mixture of
presumably difficulty separable products is obtained
(entry 13). Finally, it is interesting to note that the amino
alcohols such as 2-amino-1-ethanol (6) selectively gave
the corresponding amino ester (18) (81%) (entry 14).
No attempt has been made to probe the mechanism of
the reaction. Mechanistically, it seems plausible that the
Bayer-Villiger oxidation reaction occurs first and the
esterification step follows next. However, the reaction
failed in the absence of oxygen attempted under nitrogen
atmosphere. Thus, the aldehyde is oxidized by air in the
presence of AMA to the corresponding carboxylic acid,
which is then esterified selectively with diol. The selec-
tivity behavior of this reaction has become not clear to
us yet, and no evidence is merging for a convincing
explanation. In fact, the reaction dose not occur without
alumina and/or sulfonic acid.
(m, 3H), 8.04 (d, 2H); IR (neat) 1722 cm-1
.
2-Hydroxy-2-methylethyl benzoate (17):22 1H NMR (CDCl3,
250 MHz) δ 1.35 (m, 3H), 4.16-4.31 (t, 3H), 7.42-7.56 (m, 3H),
8.04 (d, 2H); IR (neat) 1722 cm-1
.
2-Hydroxyethyl 3-methylbenzoate (7): 1H NMR (CDCl3,
250 MHz) δ 2.37 (s, 3H), 3.94 (t, 2H), 4.43 (t, 2H), 7.19-7.37
(m, 2H), 7.83-8.18 (m, 2H); 13C NMR (CDCl3, 62.9 MHz) δ 21.49,
61.16, 67.79, 127.14, 128.59, 130.16, 130.49, 134.20, 138.46,
167.46; IR (neat) 3440, 1715, 1610, 1580, 1450, 1370, 1280, 1200,
1115, 1080, 925, 740, 680 cm-1; MS (m/e) 180 (3.5, M+), 163
(51.6), 119 (base peak), 91 (31.7). Anal. Calcd for C10H12O3: C,
66.65; H, 6.71. Found: C, 66.52; H, 6.50.
2-Hydroxyethyl 2,4-dihydroxybenzoate (9): 1H NMR
(DMSO d6, 250 MHz) δ 3.7 (t, 2H), 4.28 (t, 2H), 6.3 (s, 1H), 6.38
(d, 1H) 7.72 (d, 1H); 13C NMR (DMSO-d6, 62.9 MHz) δ 59.28,
66.79, 102.75, 104.37, 108.59, 132.18, 163.10, 164.56, 169.62; IR
(neat) 3312, 1700, 1625, 1515, 1425, 1390, 1315, 1266, 1210,
1150, 1100, 1066, 999, 900, 834 cm-1; MS (m/e) 198 (28.6, M+),
180 (32.9), 137 (74), 136 (base peak), 108 (43.9). Anal. Calcd for
C9H10O5: C, 54.55; H, 5.09. Found: C, 54.31; H, 4.97.
2-Hydroxyethyl 2-hydroxybenzoate (10): 1H NMR (DMSO-
d6, 250 MHz) δ 3.94 (t, 2H), 4.45 (t, 2H), 6.86 (m, 1H), 6.96 (m,
2H), 7.46 (m, 1H) 7.86 (m,1H); 13C NMR (DMSO-d6, 62.9 MHz)
δ 61.37, 63.92, 118.04, 119.68, 130.35, 136.21, 162.09, 170.22;
IR (neat) 3340, 1720, 1625, 1517, 1430, 1390, 1324, 1268, 1206,
1153, 1100, 1066, 997, 897, 834 cm-1; MS (m/e) 182 (20, M+),
160 (35), 121 (65), 120 (base peak), 93 (41). Anal. Calcd for
C9H10O4: C, 59.34; H, 5.53. Found: C, 59.23; H, 5.26.
2-Hydroxyethyl 4-methoxybenzoate (11): 1H NMR (CDCl3,
250 MHz) δ 3.82 (s, 3H), 3.88 (t, 2H), 4.20 (t, 2H), 6.99 (d, 2H),
7.92 (d, 2H); 13C NMR (CDCl3, 62.9 MHz) δ 55.25, 61.71, 65.90,
113.3, 120.82, 131.50, 162.48, 165.66; IR (neat) 3440, 1720, 1600,
1590, 1455, 1430, 1280, 1230, 1180, 1110, 1080, 1045, 755, 665
cm-1; MS (m/e) 196 (34, M+), 151 (62), 135 (43.2), 107 (base peak).
Anal. Calcd for C10H12O4: C, 61.22; H, 6.16. Found: C, 61.07;
H, 5.98.
2-Hydroxyethyl nicotinate (12): 1H NMR (CCl4, TMS, 250
MHz) δ 3.95 (t, 2H), 4.47 (t, 2H), 7.46 (m, 1H), 7.82 (m, 1H),
8.11 (m, 1H), 8.69 (m, 1H); 13C NMR (CCl4, TMS, 62.9 MHz) δ
61.69, 66.32, 122.61, 128.10, 136.01, 147.3, 147.6, 165.01; IR
(neat) 3400, 1725, 1590, 1495, 1452, 1310, 1293, 1250, 1124,
1075, 800, 750, 701, 665 cm-1; MS (m/e) 167 (19.9, M+), 150
(12.4), 124 (13.5), 106 (40.7), 78 (base peak), 51 (65.6). Anal.
Calcd for C8H9NO3: C, 57.48; H, 5.43. Found: C, 57.11; H, 5.24.
2-Hydroxyethyl 1-naphthoate (13): 1H NMR (CDCl3, 250
MHz) δ 3.81 (t, 2H), 4.35 (t, 2H), 7.28-7.48 (m, 3H), 7.7 (d, 1H),
7.82 (d, 1H), 8.04 (d, 1H), 8.75(d, 1H); 13C NMR (CDCl3, 62.9
MHz) δ 61.40, 66.86, 124.87-134.18, 168.08; IR (neat) 3500,
1715, 1600, 1520, 1360, 1285, 1250, 1205, 1180, 1140, 1050, 960,
790 cm-1; MS (m/e) 216 (25.1, M+), 199 (18.2), 172 (30.2), 155
(base peak), 127 (48.9). Anal. Calcd for C13H12O3 : C, 72.21; H,
5.59. Found: C, 71.98; H, 5.31.
In conclusion, the presented method constitutes the
first satisfactory method for the direct conversion of
aldehydes to glycol monoesters. Solvent-free conditions,
high yields, use of commercially available reagents,
simple workup, and high selectivity can make this
procedure a useful and attractive method for the syn-
thesis of glycol monoesters.
Experimental Section
General Procedure. To a mixture of MeSO3H 98% (1 mL,
15 mmol) and Al2O3 (acidic type 540 C, 0.27 g, 3 mmol) were
added the appropriate aldehyde (1 mmol) and then diol (1 mmol).
The mixture was stirred and heated in an oil bath at 80 °C for
2-10 h (see Table 1). The mixture was then poured into water
and extracted two times with ethyl acetate (20 mL). The organic
layer was washed with a saturated solution of sodium bicarbon-
ate (30 mL). The organic layer was dried (CaCl2) and evaporated
in vacuo to give a residue that was almost a pure glycol
monoester product. Further purification of the products was
carried out by silica gel short column chromatography.
Diethylene glycol monobenzoate (15): 1H NMR (CDCl3,
250 MHz) δ 3.72 (m, 4H), 3.85 (t, 2H), 4.50 (t, 2H), 7.41-7.59
(m, 3H), 8.06 (d, 2H); 13C NMR (CDCl3) δ 63.20, 64.91, 66.18,
68.65, 130.53, 131.82, 132.07, 135.29, 169.14; IR (neat) 3416,
2916, 1717, 1600, 1449, 1320, 1274, 1200, 1165, 1130, 1066,
1033, 890 cm-1; MS (m/e) 210 (1.1, M+), 149 (19.7), 105 (100),
77 (31.6), 45 (32.5). Anal. Calcd for C11H14O4: C, 62.85; H, 6.71.
Found: C, 62.69; H, 6.58.
2-Aminoethyl Benzoate (18). To a mixture of MeSO3H 98%
(1 mL, 15 mmol) and Al2O3 (acidic type 540 C, 0.27 g, 3 mmol)
were added benzaldehyde (1 mmol) and then 2-amino-1-ethanol
(1 mmol). The mixture was stirred and heated in an oil bath at
80 °C for 4.5 h (Table 1, entry 14). The mixture was poured into
a saturated solution of sodium bicarbonate and extracted two
times with ethyl acetate (20 mL). Then organic layer was dried
(CaCl2) and evaporated in vacuo to give 2-aminoethyl benzoate
(18) (81%): 1H NMR (CDCl3, 250 MHz) δ 3.53 (t, 2H), 3.73 (t,
2H), 4.67 (s, 2H), 7.31 (m, 3H), 7.74 (d, 2H); 13C NMR (CDCl3,
62.9 MHz) δ 43.19, 61.98, 127.44, 128.87, 130.09, 133.69, 169.19;
IR (neat) 3357, 3074, 2948, 1724, 1652, 1556, 1519, 1388, 1313,
2-Hydroxyethyl benzoate (5):22 1H NMR (CDCl3, 250 MHz)
δ 3.96 (t, 2H), 4.45 (t, 2H), 7.49-7.58 (m, 3H), 8.1 (d, 2H); IR
(neat) 1718 cm-1
.
2-Hydroxyethyl 4-methylbenzoate (6):22 1H NMR (CDCl3,
250 MHz) δ 2.39 (s, 3H), 3.88 (t, 2H), 4.41 (t, 2H), 7.2-7.31 (m,
2H), 7.91 (m, 2H); IR (neat) 1720 cm-1
.
2-Hydroxyethyl 4-chlorobenzoate (8):22 1H NMR (CDCl3,
250 MHz) δ 3.98 (t, 2H), 4.45 (t, 2H), 7.43 (d, 2H), 7.14 (d, 2H);
IR (neat) 1712 cm-1
.
2-Hydroxypropyl benzoate (14):22 1H NMR (CDCl3, 250
MHz) δ 1.99 (m, 2H), 3.78 (t, 2H), 4.45 (t, 2H), 7.41-7.58 (m,
3H), 8.05 (d, 2H); IR (neat) 1718 cm-1
.
4098 J. Org. Chem., Vol. 68, No. 10, 2003