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Synthesis of 2,5-Dimethoxybenzaldehyde

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Preparation of 4-Methoxyphenol

Quinol Monomethyl Ether3

The method of Ullmann4 for the semi-methylation of quinol (hydroquinone) was found to give poor yields and the following process was adopted after numerous trials. A solution of quinol (110 g) in sodium hydroxide (100g) and water (700 ml), contained in a flask filled with hydrogen, was cooled to 12 degrees and vigorously shaken after the addition of dimethyl sulphate (120 ml) in one portion. After about 5 minutes the mixture was cooled and the dimethyl ether collected (33g, mp 56°C). The filtrate and washings were acidified with hydrochloric acid and cooled to about 8 degrees for about 1 hour, thereafter the monomethyl ether was collected, washed with ice water, and dried (45 g., mp 52-54°C). The aqueous solution was extracted with ether and the residue after evaporation of the solvent yielded to benzene a further 30g of less pure quinol monomethyl ether, mp 41-46°C. For our purposes, it was necessary to ensure the absence of quinol from the product. The material was dissolved in benzene and any quinol which crystallized was separated; the solution was then distilled and a product, mp 53-54°C, collected at 243-246°C. This was redissolved in benzene, and the solution repeatedly shaken with small quantities of cold water. The ether was then again distilled, bp 243-244°C, mp 56°C. No coloration was developed in alkaline solution in contact with air. The substance crystallised from light petroleum has mp 56°C, but when heated to about 200°C and quickly cooled, the mp is 53°C, changing in a week or two to 55°C. Crystals, mp 56°C, also change on keeping and the mp becomes 55°C. Although these changes are small, the phenomenon is a real one.

Related are also a few older german refs for basically the same reaction sans the hydrogen atmosphere4,5,6

Hydroquinone Monomethylation7

5.0 g of hydroquinone, 40 mL of methanol and 1.0 g of cupric chloride are fed into a teflon-lined autoclave having an internal capacity of 100 mL . The autoclave is purged with nitrogen and is kept for 2.5 hours at 105°C. On termination of the reaction, an analysis of the mixture indicates the formation of 4.1 g of hydroquinone monomethyl ether (conversion 85%, selectivity 87%).

4-Methoxyphenol from Benzoquinone8

Sample
Benzoquinone
4-MeO-Phenol
Hydroquinone
After 3 h
0.12 g
14.6 g
3.6 g
After 6 h
0.00 g
15.8 g
2.8 g

Hydroquinone (18 g) and benzoquinone (2 g) in methanol (100 ml) with p-toluenesulfonic acid (5 g) were heated under reflux for 6 hours. Samples taken at 3 and 6 hours were analyzed by GLC and found to have the compositions indicated in the table.

Formylation of 4-Methoxyphenol

Formylation of 4-Methoxyphenol (4-hydroxyanisole, hydroquinone monomethyl ether) yields 2-Hydroxy-5-Methoxybenzaldehyde (5-Methoxysalicylaldehyde). The most promising procedures include Reimer-Tiemann formylation (CHCl3/KOH) and Mg-mediated phenol ortho-formylation with paraformaldehyde. A few variations on this theme is presented below.



Formylation with Paraformaldehyde/Magnesium Methoxide

Written by DTT, Translation from Russian by Dioulasso

This formylation method can be a superior alternative to the much discussed Reimer-Tiemann formylation (a selective ortho-formylation of phenols).

Experimental

A 2000 mL RBF equipped with a reflux conenser, a mechanical stirrer, and an addition funnel is charged with 32g of magnesium followed by 200ml dry Methanol. It is possible to ad more MeOH so Mg dissolves faster. The reaction is vigorus. Sometimes the flask has to be cooled to prevent the condenser from spitting around. When the mixture is beginnig to get thick, 250g of 4-methoxyphenol in 300-500ml of hot toluene is added in a slow stream from the addition funnel. The mixture is heated up with good stirring. (Watch out - the precipitated phenolate can stick to the bottom).

When all the magnesium has dissolved, the MeOH is evaporated (it is also possible not to evaporate allNote 1). A suspension of 180g of ParaformaldehydeNote 2 in Toulene is added in small portions every 10 minutes (exotermic!), with good stirring of the thick mixture. This takes about an hour. The mixture turns yellow and gets less thick. The mixture is than stirred for another 30 min and acidified with dilute Sulfuric AcidNote 3. The toluene layer is separated and the toluene is driven off. The rest is 2-Hydroxy-5-Methoxy-Benzaldehyde.

The thus obtained product is not contaminated with 4-methoxyphenol, but containes the dimer as an inpurity. It may be cleaned via the bisulphite adduct or it can be distilled under reduced pressure. Yield is around 80%. The aldehyde may stain the skin yellow.

Notes:

  1. IMHO it is not necesseary…Once I have tried not to evaporate all of it and all seemed to work fine.
  2. Dry paraformaldehyde was used.
  3. In the patent the acidified mixture is stirred for 5h. I'm not sure about that half an hour figure - just act by the situation. You can see the decomposition of phenolate visually as it dissolves in toluene. One has to scratch it diligently off the flask's wall, though.

Some final notes by Dioulasso:



Magnesium-mediated ortho-formylation of phenols1

2-OH-5-MeO-benzaldehyde from 4-MeO-phenol, Mg(OMe)2, and paraformaldehyde in MeOH/toluene. Yield: 97% The procedures are described for (nonyl)Phenol, simply use an equimolar amount of 4-Methoxyphenol instead.

Experimental

Phenol (37.6 g, 0.4 mol) was added to magnesium methoxide (259 g of 8% (w/w) solution in methanol; 20.7 g, 0.24 mol) and the mixture was heated to reflux. Approximately half of the methanol was distilled off and toluene (300 g) was added to the residue. The azeotropic mixture of toluene and and methanol was removed by fractional distillation, until the temperature of the reaction rose to 95°C. A slurry of paraformaldehyde powder (43.2 g, 1.44 mol) in toluene (75 g) was added in small portions over 1 h to the reaction mixture at 95°C with concurrent removal of the volatile materials by didtillation. Stirring was continued at 95°C for 1 h, after which the mixture was cooled to 25°C and added slowly to 10% sulfuric acid (450 g), The resulting mixture was stirred at 30-40°C, after which the aqueous layer was separated and extracted with toluene (2x100 g). The combined organic layers and extracts were washed with 10% sulfuric acid (50 g) and water (50 g) and evaporated under reduced pressure to give the aldehyde as a pale yellow oil (48.35 g, 84% w/w by GC and 1H-NMR comparisn against a reference standard and against a commercial sample of known purity; 83% yield).

In similar reactions they used the following conditions:

Magnesium raspings (7.3 g, 0.3 mol), methanol (112 g), toluene (48.5 g) and magnesium methoxide (1.6 g of 8% w/w solution in methanol; 1.5 mmol) were heated under reflux for 2 h untile the magnesium had dissolved and hydrogen evolution had ceased. 4-Nonylphenol (112 g, 0.5 mol) was added to the mixture [...]



Convenient method for the ortho-formylation of phenols2

2-OH-5-MeO-benzaldehyde from 4-MeO-phenol, MgCl2, Et3N, and paraformaldehyde in MeCN.
Yield: 97% Reaction time: 2 h

Phenolic derivs. are formylated selectively ortho to the hydroxy group by paraformaldehyde with magnesium dichloride-triethylamine as base. With alkyl-substituted phenols, e.g., 2-, 3-, 4-Methylphenols, excellent yields of the corresponding salicylaldehyde derivs. were obtained. Similar results were obtained with 2-, 3-, and 4-chloro-substituted phenols and with 3-and 4-methoxyphenol, while 2-methoxyphenol was unreactive. A good yield of Methyl 3-formyl-4-hydroxybenzoate was obtained by this method as well, but generally phenols with electron-attracting groups reacted sluggishly; the long reaction times required caused the formation of byproducts, particularly MOM-derivs. of the phenols.

General procedure:

Dry (P2O5) paraformaldehyde (135 mmol) was added to a mixture of the phenolic derivative (20 mmol), commercially available anhydrous magnesium dichloride (30 mmol) and dry (Na) triethylamine (75 mmol) in acetonitrile (100 mL; distilled over CaH2), and the mixture was heated under reflux for the reaction time recorded. The mixture was cooled to room temperature after which 5% aq. HCl was added and the product extracted with ether. The dried (MgSO4) extract was evaporated and the residue purified by flash chromatography on silica gel.

3-Hydroxy-Benzaldehyde to 2,5-dihydroxybenzaldehyde

Neubauer and Flatow9 prepared 2,5-dihydroxybenzaldehyde by the oxidation of salicylaldehyde but the present method with m-hydroxybenzaldehyde as initial material gives an improved yield of a less crude product.

Experimental10

A solution of m-hydroxybenzaldehyde (61 gr) and NaOH (25 gr) in water (400 cc), while being vigorously stirred and kept at 30-35°C, is treated simultaneously from separate dropping funnels with aqueous solutions of potassium persulphate (150 gr in 1500 cc) and NaOH (200 cc, 40%), the additions being made during 90 min. at such rates that the mixture is always alkaline. After 36 hours of standing, the deep brown solution is rendered faintly acidic (Congo Red paper), and unchanged m-hydroxybenzaldehyde (31 gr) is extracted with ether. The solution is then strongly acidified (350 cc of conc HCl) and heated slowly to 70°C, the dark brown amorphous precipitate which forms gradually, being filtered off (this substance, which chars above 330°C, is almost insoluble in all organic solvents, but readily soluble in aq. Na2CO3 - it contains the aldehyde group as shown by the formation of the p-nitrophenylhydrazone, and invariably constitutes about 40% of the yield). The 2,5-dihydroxybenzaldehyde is extracted from the filtrate by ether, ether removed by evaporation, and the residue extracted by benzene. Yield 13g, mp 89-92°C. This substance crystallises from benzene in bright yellow needles, but they still contain solvent. They rapidly effloresce at room temperature, leaving yellow needles, mp. 98-99°C.

Gentisinaldehyde could not be obtained from 2-nitro-5-hydroxybenzaldehyde by reduction, diazotisation and decomposition of he azo-compounds. The latter however could be obtained in 30% yield.

2-Hydroxy-5-Methoxybenzaldehyde
to 2,5-Dimethoxybenzaldehyde

Written by Antoncho

4,7 g of crude dark-brown 2-hydroxy-5-MeO-benzaldehyde obtained by Reimer-Tiemann formylation (steam-distilled) was placed into a 150ml three-necked RBF. There was added 25mls dioxane (undried, but kept over FeSO4 to remove peroxides), 5g freshly fused potassium carbonate, 1ml MeOH (Note 1) and, at last, 2mls (4,6g = 25% molar xcess) methyl iodide. The central neck of the flask was fitted w/a condenser, one of the side-necks - w/a thermometer, and the 3rd one was plugged to bee later used for various tests and additions. The apparatus was flushed w/butane and all was brought to a very gentle reflux on a waterbath.

The temp, measured inside the boiling liquid, at first was ~77°C, increased to 85°C in ~30mins, and went up to 92°C over the next 3 hours. Boiling was cont'd overnight (Note 2)

An aliquot of the liquid was taken w/a syringe, acidified, evaporated under draught to remove carcinogenic dioxane and smelled. The specific smell of unreacted starting material was apparent, mixed w/a somewhat similar, but sweet, aroma of p-diMeO-benzene (Note 3).

So 0,7mls of MeI were added and reflux recommenced. After 4 hrs (internal temp 92°C) another test was taken which again indicated the presence of the starting material. Another 0.7 mls MeI were added and refluxed for several more hours; the third test revealed the completion of the rxn.

The rxn was flooded with 60 ml of 20% KOH, saturated w/NaCl and xtracted w/30+15 mls of IPA. Alcohol was separated, some 10g of Na2SO4 were added in a faint attempt of drying, followed by 90mls of saturated aq. metabisulfite. The mixtr was subjected to vigorous mech stirring for 7 min and the precipitate (which ended up in the alcohol layer) was filtered, washed twice with a lil IPA to almost completely remove yellow coloration (Note 4), pressed between filter paper and somewhat dried under draught. Still containing some IPA, it weighed 8.7g.

Thus obtained adduct was thrown into 50mls of pre-chilled in the freezer 20% KOH, stirred and left for 30 mins in warm water (Note 5). Precipitated aldehyde was filtered, washed with water 3 times, pressed between filters as dry as possible, chopped on a plate and left to air-dry. Still containing a little water, it was off-white, but still pretty, vanillin-like powder without any noticeable smell and weighed 3.6g (Note 6). After drying it was 2.7g.

Notes

  1. Dioxane was chosen for the following reasons:
    1. a much higher bp as compared to acetone
    2. unreactivity towards the carbonyl group, which is a possible disadvantage of using acetone
    3. ability to dissolve both MeI and, to some xtent, alkali.

    The rationale beehind addind MeOH was the following: K2CO3 reacts with it to form KHCO3 and KOCH3. The latter, being more soluble than K2CO3, was supposed to act as sort of a PTC. Unfortunately, it later turned out that SWiHKAL's MeOH was VERY wet (not to mention water in dioxane), so the effectiveness of this additive remains to bee researched. In any case, the two-fold amt of MeI that was required for the rxn, warrants further investigation. Probably, unhydrous conditions would bee better. Maybee, methanol shouldn't bee added at all - to minimize hydro/methanolysis of MeI, which is the major side rxn.
  2. Probably, there is no need to reflux the mixture more than 30-60 min after the internal temp reached maximum. SWiHKAL just wanted to bee sure.
  3. p-MeO-phenol is a major impurity contained in the hydroxyaldehyde isolated by steam-distillation from a RT formylation. It's hard to estimate, but there is quite a bit of it in there, probably not less than 20%.
  4. This intensely colored yellow impurity is, probably, benzoquinone which survives all the transformations since its usage in methylation of hydroquinone. The next time SWiHKAL does that, he'll first try to remove it with bisulfite from the crude p-MeO-phenol.
  5. SWiHKAL wanted to make sure all adduct decomposed. Since the appearance of the substance virtually doen't change, several tests were needed to confirm that. However, decomposition of the adduct seems to proceed fast even w/cold KOH.
  6. The mp was measured and found to bee circa 45°C, whereas the lit value is 51°C. Could anyone suggest to what kind of (im)purity that corresponds?

References

  1. R. Aldred et al., J. Chem. Soc. Perk. Trans. I, 1823 (1994)
  2. N. U. Hofsløkken, L. Skattebøl, Acta Chem. Scand. 53, 258 (1999)
  3. J. Chem. Soc. 393 (1926)
  4. Ullmann, Annalen 327, 116 (1903)
  5. Helvetica Chimica Acta, 7, 951
  6. Monatsheft, 45, 581
  7. US 4,469,897 (Ex. #2)
  8. US 4,294,991 (Ex. #20)
  9. Neubauer and Flatow, Z. Physiol. Chem. 52, 375 (1907)
  10. J. Chem. Soc. 2339 (1927)

Further Preparations of 4-Methoxyphenol

Chem. Abs. 95:61763
Hydroquinone monomethyl ether.
Pokrovskaya, I. E.; Parbuzina, I. L.; Gubenko, I. I. (USSR ). U.S.S.R. SU 825487 30 Apr 1981 From: Otkrytiya, Izobret., Prom. Obraztsy, Tovarnye Znaki 1981, (16), 93. (Russian).

Hydroquinone (I) mono-Me ether was prepd. by treating I with a neutral soda mixt. of MeOH and H2SO4 at 90-100°C. In an improved procedure, the reaction was carried out in the presence 4-10 wt.% I di-Me ether, which was recycled.

Chem. Abs. 93:71276
Preparation of hydroquinone ethers.
Bellas, Michael; Cahill, Robert; Hayes, Leslie (Kodak Ltd., Engl.). Brit. GB 1557237 5 Dec 1979, 8 pp. (English).

The title ethers I [R = C1-C18 alkyl, (CH2)2OEt; R1 = H, C1-4 alkyl] were prepd. by reaction of a mixt. of the corresponding hydroquinone and benzoquinone (wt. ratio 5:1 to 20:1) with ROH in the presence of an acid dehydration catalyst. E.g., reaction of 0.67 g benzoquinone and 9.33 g hydroquinone with 50 mL MeOH in the presence 10 g conc. H2SO4 gave 80% I (R = Me, R1 = H).

Chem. Abs. 1:140564
Hydroquinone monoalkyl ethers.
(Eastman Kodak Co., USA). Jpn. Kokai Tokkyo Koho JP 54061132 17 May 1979 Showa, 4 pp. (Japanese).

Ethers I (R = alkyl, R1 = H, alkyl; R2 = R3 = H or R2R3 = CH=CHCH=CH) were prepd. by esterification of I (R = H; R1-R3 as above) with alcs. ROH in the presence of benzoquinones II (R1-R3 as above) and acidic dehydrating agents. Thus, stirring I (R-R3 = H) in MeOH with benzoquinone and H2SO4 16 h gave 100% I (R = Me, R1-R3 = H).

Chem. Abs. 90:168271
p-Methoxyphenol.
Gubenko, I. I.; Kondrashova, M. F.; Manyashkina, V. M.; Medvedeva, S. P.; Parbuzina, I. L. (USSR ). U.S.S.R. SU 643489 25 Jan 1979 From: Otkrytiya, Izobret., Prom. Obraztsy, Tovarnye Znaki 1979, (3), 84. (Russian).

p-MeOC6H4OH was prepd. by methylating hydroquinone with MeOH-H2SO4-Na2CO3 (1.3:1:1) at 90-100°C.

Chem. Abs. 89:208651
Solvent composition effects in reversed phase partition chromatography. I. Phenols in systems of the type oleyl alcohol-water + acetone or water + acetonitrile.
Soczewinski, Edward; Waksmundzka-Hajnos, Monika; Chem. Anal. (Warsaw), 23(3), 429-35 (English) 1978.

The relation between RM values of 28 phenols and the concn. of Me2CO or MeCN in the aq. mobile phase was investigated; the stationary phase was Whatman no. 4 paper impregnated with C6H6 solns. of oleyl alc. In most cases the relations were linear, which permitted the detn. of the RM values beyond the range of optimum accuracy by extrapolation

Chem. Abs. 105:104738
Electrochemical synthesis of hydroquinone monoalkyl ethers.
Takamatsu, Hideki; Takakuwa, Yasuo; Tsuchiya, Shuji (Nissan Chemical Industries, Ltd., Japan). Jpn. Kokai Tokkyo Koho JP 61064891 A2 3 Apr 1986 Showa, 4 pp. (Japanese).

Hydroquinones and alcs. are electrolyzed for monoalkylation to give hydroquinone monoalkyl ethers. The ethers, useful as intermediates for medicines, agrochems., dyes, etc., are obtained selectively at high yield. Thus, hydroquinone and was dissolved in EtOH and electrolyzed, using Pt electrodes, for 18 h at 30 V and ~30°C (12,000 C electricity) to give hydroquinone monoethyl ether at 86% conversion, 99% selectivity, and 85% yield. No byproduct (hydroquinone di-Et ether) was obtained.

Chem. Abs. 104:87782
Study of the steam distillation of phenolic compounds using ultraviolet spectrometry.
Norwitz, George; Nataro, Nicole; Keliher, Peter N.; Anal. Chem., 58(3), 639-41 (1986)

The steam distn. of 42 phenolic compds. was studied using a semimicro steam-distn. app. and UV spectrometry. In the distn., the following gave >95% recoveries: PhOH, 2-RC6H4OH (R = O2N, MeO, Br, Cl), 2,3- and 2,4-Cl2C6H3OH, 2,4,5- and 2,4,6-Cl3C6H2OH, 2,4-Br2C6H3OH, 2-, 3- and 4-cresol, 4,2-Cl(Me)C6H3OH, 2,4-, 2,5-, 2,6-, 3,4- and 3,5-xylenol, 4-RCMe2C6H4OH (R = Me, Et), thymol and carvacrol. The percent recovery for the other phenolic compds. was as follows: 3-O2NC6H4OH, 3.7%; 4-O2NC6H4OH, 1.8%; 3-MeOC6H4OH, 31.1; 4-MeOC6H4OH, 23.2; 3-BrC6H4OH, 79.6; 4-BrC6H4OH, 67.8; 3-ClC6H4OH, 93.5; 4-ClC6H4OH, 91.6; 3,4-Cl2C6H3OH, 64.1; 2,4-(O2N)2C6H3OH, 21.2; picric acid, 0.0; 2-H2NC6H4OH, 0.1; 3-H2NC6H4OH, 0.2; 4-H2NC6H4OH, 0.1; pyrocatechol, 1.6; resorcinol, 0.4; hydroquinone (I), 0.0; pyrogallol, 0.7; and phloroglucinol, 0.1. Examg. the spectra of the undistd., distd. and residual solns. showed that the aminophenols undergo some decompn., and that I is almost completely destroyed during the distn. The important role that H bonding (intermol. and intramol.) plays in the recovery from steam distn. is examd

Chem. Abs. 97:91924
Monoalkyl ethers of hydroquinone and its derivatives.
Rivetti, Franco; Romano, Ugo; Di Muzio, Nicola US 4469897

The title compds. I (R = alkyl, R1 = H, alkyl) were prepd. by treating a hydroquinone I (R = H) with ROH in the presence of a transition metal salt. A mixt. of 1,4-(HO)2C6H4, MeOH, and CuCl2 under N2 kept 2.5-4 h at 105°C gave I (R = Me, R1 = H) in 87% selectivity with 55-85% conversion. Little or no etherification occurred in the absence of CuCl2.

Chem. Abs. 112:136225
Defense mechanisms of arthropods. Part 91. p-Methoxyphenol: chemical basis of stench of a female butterfly.
Eisner, T.; Eisner, M.; Jaouni, T.; Fales, H. M.; Naturwissenschaften, 77(1), 33 (English) 1990.

The female Great Southern White butterfly (Ascia manuste phileta) emits a potent phenolic stench when disturbed. The odor stems from a pasty secretion from the genitalia. Gas chromatog./mass spectrometry identified this defensive compd. as p-methoxyphenol.

Chem. Abs. 106:226806
Steam distillation of phenolic compounds in the presence of a large amount of sodium chloride.
Norwitz, George; Nataro, Nicole; Keliher, Peter N.; Microchem. J., 35(2), 240-3 (English) 1987.

The steam distn. of phenolic compds. in the presence of a large amt. of NaCl was studied by use of a semimicro steam distn. app. and UV spectrometry. The recovery of many phenolic compds. in steam distn. was improved by the addn. of the NaCl, particularly in the case of 3- and 4-methoxyphenol, 3- and 4-bromophenol, and 3- and 4-chlorophenol (essentially complete recovery was obtained with the latter four compds.). The recovery with 2-chlorophenol was ~5% lower. The recovery with 2-nitrophenol was ~10% lower and the results tended to be erratic (probably because the NaCl affects the intramol. H bonding of this polar compd.). The addn. of NaCl did not improve the very low recoveries obtained with aminophenols and di- and trihydroxyphenols without NaCl. It is recommended that NaCl be used in the detn. of total phenolic compds. in waters in procedures that require a steam distn., since more complete recovery is obtained for the phenolic compds. that are likely to be found in waters.

Chem. Abs. 125:167560
Preparation of 4-alkoxyphenols from 1,4-dihydroxybenzene.
Saito, Toranosuke; Hirayama, Takumi; Sakaguchi, Shigeo (Sanko Kaihatsu Kagaku Kenk, Japan). Jpn. Kokai Tokkyo Koho JP 08151343 A2 11 Jun 1996 Heisei, 5 pp. (Japan).

4-HOC6H4OR (I; R = lower alkyl), useful as polymn. inhibitors for vinyl monomers, stabilizers for polyesters, and intermediates for drugs, agrochems, and, dyes are prepd. by addn. of H2O2 to a mixt. of 1,4-C6H4(OH)2 (II), ROH, and ³1 of I, HI, metal iodides, and alkali metal iodates followed by addn. of acid catalysts or by addn. of H2O2 to a mixt. of II, ROH, ³1 of HI, metal iodides, and alkali metal iodates, and acid catalysts. An aq. H2O2 soln. was added dropwise to a mixt. of II, MeOH, H2SO4, and I at 60°C over 3 h and the reaction mixt. was further stirred at 60-70° for 6 h to give a product contg. 87.3% I (R = Me), vs. 54% for a control using no I.

Chem. Abs. 125:86240
Methods for the preparation of hydroquinone monomethyl ether.
Teng, Dianhua; Li, Tongzhen; Ma, Shuqin (Inst. Petrochem., Heilongjiang Acad. Scis., Harbin 150040, Peop. Rep. China). Huaxue Yu Nianhe, (2), 105-106 (Chinese) 1996.

A review with 9 refs. on different methods for prepn. of hydroquinone monomethyl ether with the emphasis on the methods using hydroquinone and methanol as raw materials, an acid as catalyst, and benzoquinone as co-catalyst

Chem. Abs. 124:260570
Process for the preparation of hydroquinone monoalkyl ethers.
Caproiu, Miron Teodor; Banciu, Anca Adriana; Olteanu, Emilia. RO 105090 (1994), 5 pp. (in Romanian).

The title ethers were prepd. by treating hydroquinone with an alc. in presence of an oxidizing agent and a dehydrating agent in the alc. as solvent, or using another solvent. Thus, hydroquinone was treated with MeOH, H2O2, and H2SO4 under reflux for 6 h to give 70.5% 4-Methoxyphenol of 98.7% purity.

Chem. Abs. 121:270800
Effect of substituted groups on the retention of monosubstituted phenols in reversed-phase liquid chromatography.
Kim, Hoon-Joo; Lee, In-Ho; Lee, Dai Woon (Anal. Sci., R and D Cent., Daejeon 305-343, S. Korea). J. Korean Chem. Soc., 38(8), 562-9 (Korean) 1994.

The retention data of twenty one monosubstituted phenols in the eluent systems contg. 30-70% of methanol or acetonitrile as org. modifiers, on C18 and Ph columns were collected to study the effect of the substituted groups on the retention of phenols. The capacity factors of the solutes except amino phenols are greater on C18 than on Ph column. And all the solutes showed greater capacity factors in methanol-water than that in acetonitrile-water as a mobile phase. Generally the elution order between meta and para isomers of monosubstituted phenols in consistent (p < m) regardless of the polarity of the substituted group. But the elution order between ortho and meta isomers of phenol varies with regard to the polarity of the substituted group. The retention of the monosubstituted phenols was influenced by the interaction between the solute and unreacted silanol of columns as well as the interaction between the solute and C18 or Ph group of columns. The effect of unreacted silanol on the retention of the monosubstituted phenols is greater on C18 than on Ph column. The greater hydrogen bonding acceptor basicity(b) of the substituted group is, the greater this effect is. The relation between the retention of the monosubstituted phenols and their parameters such as van der Waals vol. (VWV) and hydrogen bonding acceptor basicity(b) was studied. The good linearity was obsd. in the plot log k' vs. (1.1VWV/100-1.84b). In consequence, the retention of the monosubstituted phenols on C18 and Ph columns can be easily predicted by the parameter (1.01VWV/100-1.84b)

Chem. Abs. 118:124199
Etherification of phenols with lower alcohols.
Uohama, Misao; Takahashi, Katsuji (Dainippon Ink and Chemicals, Inc., Japan). Jpn. Kokai Tokkyo Koho JP 04305546 A2 28 Oct 1992 Heisei, 6 pp. (Japan).

Phenols are etherified with lower alcs. in liq. phases in the presence of acid catalysts with removing alkyl ethers together with unreacted alcs. and H2O by distn. Catechol and concd. H2SO4 were heated at 150° with adding MeOH-catechol mixt. for 6 h to give 88.4% guaiacol

Chem. Abs. 127:81239
Process and catalysts for the production of alkyl ethers of phenols from phenols and alkanols.
Ariyoshi, Kimio; Satoh, Yuuichi; Saito, Noboru (Nippon Shokubai Co., Ltd., Japan). Eur. Pat. Appl. EP 781751 A1 2 Jul 1997, 16 pp. DESIGNATED STATES: R: DE, FR, GB, IT. (European Patent Organization).

Alkyl ethers of phenols (e.g., anisole) are prepd. in high yield and selectivity by the etherification of a phenol (e.g., PhOH) with an alkanol (e.g., MeOH) in the presence of an oxide catalyst comprising a supported alkali metal (e.g., Cs) as a constituent element.

Process for the preparation of 4-alkoxyphenols
DE 3207937 (March 5, 1982)

A novel process for the preparation of 4-alkoxyphenols by reacting hydroquinone with an alcohol at increased temperatures in the presence of catalytic amounts of benzoquinone and an acid is characterised in that perchloric acid is used as the acid. This process gives 4-alkoxyphenols in high yields. 4-Alkoxyphenols are valuable intermediates, for example for the preparation of 4-alkoxyphenyl carboxylates, which are used as liquid-crystalline compounds.