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The programme examines a multi-stage synthesis and those criteria which determine choice of routes, reactions, starting materials, etc. The product of the synthesis is B-methylstyrene.
Metadata describing this Open University video programme
Item code: S24-; 09
First transmission date: 13-05-1972
Published: 1972
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Duration: 00:24:40
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Producer: David Jackson
Contributors: Len Haynes; David Roberts
Publisher: BBC Open University
Keyword(s): B-methystyrene from n-propanol; Chemical analysis; Extraction; Isomers; Methods; Multistage synthesis; Reagents; Side reactions; Yields
Footage description: Len Haynes introduces the programme. D.R. Roberts works out two routes for synthes for B-methylstyrene from n-propanol. The routes are shown on a mag-board diagram. (Convergent and linear routes) Roberts compares the two routes. On paper the convergent route looks more promising. The convergent route is tested in the laboratory by Barrie Whatley. He oxidises n-propanol to propionaldehyde with acid dichromatic solution. Whatley then dries the product by adding molecular sieve pellets to the solution. The resulting yield is 35%. Roberts, with the mag-board showing the convergent route, explains the disadvantages of the above reaction. Barrie Whatley continues with his demonstration of the second part of the convergent route synthesis, the preparation of the Grignard reagent and its condensation with proprionaldehyde to form 1-phenylpropanol. Whatley explains each step of the synthesis. Roberts discusses the advantages of Grignard reactions with the aid of a diagram which shows the products of these reactions. Whatley tests the linear route in the laboratory. He begins by explaining and demonstrating the alkaline permanganate method of oxidising propanol to propanoic acid. The yield is 76%. Whatley next explains and demonstrates the conversion of propanoic acid to propanoyl chloride by reaction with solid phosphorous pentachloride. A yield of 86% propanoyl chloride is obtained by this method. Whatley explains and demonstrates the preparation of propanophenone by Friedel-Crafts reaction. The product is extracted after several distillations. Whatley next demonstrates the reduction of propanophenone to 1-phenylpropanol. He stirs propiophenone with lithium aluminium hydride in an inert solvent (benzene). The yield of 1-phenylpropanol is virtually 100% by this method. Shot of a chart showing the boiling points of the products at each stage of the linear route. Whatley explains how this is used to help identify the compounds produced. Roberts explains why infra-red spectroscopy can help to identify the compounds of the reactions. Whatley with infra-red spectrographs of all the compounds made during the synthesis. He examines the last product of the linear route synthesis and then compares this with the spectrum of the last compound from the converged route synthesis. They are identical. Roberts compares the yield from the two routes. In practice the linear route synthesis is more efficient. Roberts looks for ways of improving the yields and suggests that the linear route can be improved in the Friedel-Crafts reaction. Whatley demonstrates the dehydration of 1-phenylpropanol to give B-methylstyrene. Roberts explains that reactions, such as the acid catalysed dehydration above, often give rearranged products and that the product of the above reaction may not be pure B-methylstyrene. He points out that it may be a mixture of isomeric olefins. Whatley separates the product of the last reaction by gas chromatography and examines the trace. Roberts considers three possible isomers which may be the products of the dehydration experiment Gamma - methylstyrene, Beta - methylstyrene and allylbenzene). Roberts then explains why infrared spectroscopy would not help to identify the products unless comparison spectra were available. Roberts explains that ultra-violet spectroscopy eliminates the allylbenzene as a possible product. Roberts explains why the degradation method is useful for identifying the product. He explains this method using a blackboard and chalk. The major product (95%) is in fact B-methylstyrene. Roberts sums up the characteristics of the minor product (5%) of the synthesis. He asks students to think of any possible type of isomerism which was not considered in the programme.
Master spool number: 6LT/70381
Production number: 00521_2172
Videofinder number: 1726
Available to public: no