2CB via the cinnamonitrile
(Rated as: good read)
Tricky Post 289500 (Tricky: "NB! we need just 3-carbon chain !", Methods Discourse) and Otto Post 289892 (otto: "some remarks", Methods Discourse) put together a couple of good posts a while back for a route to 2CB via the cinnamonitrile. Well, here's another reference of the same kind. Anyone fancy this route to their favourite phenethylamine?
Organic Syntheses, CV 7, 108 [http://www.orgsyn.org/]
SYNTHESIS OF alpha,beta-UNSATURATED NITRILES FROM ACETONITRILE: CYCLOHEXYLIDENEACETONITRILE AND CINNAMONITRILE
Preparation of E- and Z-Cinnamonitrile. A 1-L, three-necked, round-bottomed flask equipped with a mechanical stirrer, reflux condenser, and addition funnel s charged with potassium hydroxide pellets (33 g, 0.5 mol) and acetonitrile (400 mL). The mixture is brought to reflux under nitrogen and a solution of benzaldehyde (53 g, 0.5 mol) in acetonitrile (100 mL) is added in a stream (1–2 min). After addition, stirring is continued for 10 min* and the hot solution is then poured onto 500 g of cracked ice in a 1-L beaker. After being cooled for a few minutes, the two-phase mixture is transferred to a 2-L, three-necked flask and steam-distilled**. The distillate is transferred to a separatory funnel, and the upper aqueous phase is separated and then extracted with two 500-mL portions of ether***. The combined organic material is dried briefly over Na2SO4 and the ether evaporated to yield pure cinnamonitrile (20–29 g, 31–45%) as a pale-yellow oil (E/Z ratio ca. 5.5).
Notes. * Potassium hydroxide (85% pellets, AR grade) should be as fresh as possible. The reaction time depends on the quality of the potassium hydroxide employed. An induction period is often observed when older potassium hydroxide samples are used, possibly because surface formation of carbonates reduces the solubility of the salt in acetonitrile. An attempt was made to monitor the cinnamonitrile reaction by GLC, following loss of starting material. Although formation of the product was observed and reached a maximum, the starting material peak never completely disappeared. Prolonged reaction times (>2 hr) resulted in failure to isolate any of the desired product. Reaction times of less than 30 min gave the expected yields. Undissolved potassium hydroxide was observed in the reaction vessel when these reactions were terminated. ** Steam distillation may be conducted using apparatus designed either for internal or external steam generation. Using internally generated steam, 2.5 L of distillate was collected. The last 500 mL contained less than 1 g of product. *** To facilitate phase separation, solid sodium chloride was added to the aqueous layer.
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