Methylthiomethylation of Vanillin: Help understanding a French procedure
Hello,
After considerable effort I was able to find the following paper (attached below) which describes the 5-methylthiomethylation of vanillin in decent
yield simply by heating the two together.
All the alternate procedures require an activating agent (thionyl chloride, trifluoroacetic acid anhydride, and- interestingly- tBuBr) but there seems
to be a selectivity issue on whether the phenol itself or the aromatic ring is the nucleophile attacking in the Pummerer rearrangement, as well as
confusion on the mechanism (Is there an electrophilic substitution, or a [2,3]-sigmatropic rearrangement of an ylide? These, to the best of my
understanding, should require different reagents).
This benzyl thiomethyl ether should be an interesting intermediate: it can be desulfurated to the methyl, chlorinated and hydrolyzed to the aldehyde
(but I suspect there are multiple routes from this as a net formylating reaction), and (curiously) with Cu(ii)Cl2/ZnCl2 undergoes Friedel-Crafts
alkylation type reactions with anisole
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Anyway, here is the relevant excerpt, followed by the machine translation:
| Quote: |
PARTIE EXPÉRIMENTALE. Le DMSO employé anhydre, pur, est de qualité courante du commerce. Les composés étudiés sont traités en solution dans le
DMSO à ébullition sous reflux pendant 3 h. La solution est alors extraite par entraînement à la vapeur d'eau, ce qui permet de récupérer une
fraction entraînable, non miscible à l'eau. Celle-ci est analysée par chromatographie en phase gazeuse, sur de 180 cm, d'un diamètre inférieur de
5 mm, remplie de chromosorb W, AW-DMCS imprégné de 10 % en poids de silicone SE 30. La température de l'analyse est de 100°C, avec un débit de
gaz vecteur (He) de 75 ml/mn. Après cet entraînement à la vapeur, l'addition d'eau dans la proportion de 1 à 5, à la solution dans le DMSO,
produit un précipité abondant. Après lavage, ce dernier, reprise de nouveau par du DMSO, subit un nouvel entraînement à la vapeur d'eau, suivi
d'une nouvelle précipitation. Le produit est finalement purifié par recristallisation à partir d'une solution dans un mélange eau-éthanol de
proportion 50/50. L'analyse des produits obtenus par chromatographie en couche mince, ne donne qu'une seule tache. une colonne d'une longueur
Vanilline. - Le traitement de 5 g de vanilline par 5o ml de DMSO conduit à l'obtention de 3,08 g de produit brut, soit un rendement de 61,2 %. Après
recristallisation, nous obtenons 2,28 g d'un produit ne donnant qu'une tache par analyse chromatographique sur couche mince. Plusieurs analyses sont
faites, l'une d'entre elles sur poudre de cellulose, éluée par une solution de butanol, elle-même saturée par une solution 1,5 N d'ammo- niaque,
présente un R, de 0,78. Le produit obtenu a un point de fusion de 92°C. Analyse : C1. H420,S, calculé %, C 56,60; H 5,66; S 15,10; trouvé %, C
55,79; H 5,61; S 14,76. |
| Quote: |
EXPERIMENTAL PART. The anhydrous, pure DMSO used is of current commercial quality. The compounds studied are treated in solution in DMSO at boiling
point under reflux for 3 h. The solution is then extracted by steam entrainment, which makes it possible to recover a drivable fraction, immiscible
with water. This is analyzed by gas chromatography, over 180 cm, with a diameter less than 5 mm, filled with chromosorb W, AW-DMCS impregnated with
10% by weight of silicone SE 30. The temperature of the analysis is 100 ° C, with a carrier gas flow rate (He) of 75 ml / min. After this steam
entrainment, the addition of water in the proportion of 1 to 5, to the solution in DMSO, produces an abundant precipitate. After washing, the latter,
taken up again with DMSO, undergoes a new entrainment with steam, followed by a new precipitation. The product is finally purified by
recrystallization from a solution in a 50/50 water-ethanol mixture. Analysis of the products obtained by thin layer chromatography gives only one
spot. a Vanillin-length column. - The treatment of 5 g of vanillin with 50 ml of DMSO leads to obtaining 3.08 g of crude product, ie a yield of
61.2%. After recrystallization, we obtain 2.28 g of a product giving only one spot by chromatographic analysis on a thin layer. Several analyzes are
carried out, one of them on cellulose powder, eluted with a butanol solution, itself saturated with a 1.5 N ammonia solution, has an R of 0.78. The
product obtained has a melting point of 92 ° C. Analysis: C1. H420, S, calculated%, C 56.60; H 5.66; S 15.10; found%, C 55.79; H 5.61; S
14.76. |
My question is what exactly is the extraction procedure calling for? Steam distillation? What is a drivable fraction? If I understand correctly,
vanillin is steam distilled off, then the methylthiomethylated product crashed out w/ water, and steam distilled once more, repeated until no more
vanillin is carried off by steam. Is this correct? Seems inconvenient, but far better than thionyl chloride, I guess.
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[Edited on 24-12-2019 by myr]
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