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Alcohols and derivatives

Alcohols and derivatives. What are alcohols and what are they used for?. Answers Solvents –to dissolve other chemicals in them for reactions As a widely used solvent for paint, varnish and drugs, Fuels –ethanol is used as a replacement for petrol (e.g. in Gasahol),

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Alcohols and derivatives

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  1. Alcohols and derivatives

  2. What are alcohols and what are they used for? • Answers • Solvents –to dissolve other chemicals in them for reactions • As a widely used solvent for paint, varnish and drugs, • Fuels –ethanol is used as a replacement for petrol (e.g. in Gasahol), • In the manufacture of ethanal, (i.e. acetaldehyde), and ethanoic acid, (i.e. acetic acid), • Used to make esters and polyesters • Antifreeze for cars –highly appropriate for Qatar • In the manufacture of alcoholic drinks, e.g. Vodka, etc., • As the fluid in thermometers • In preserving biological specimens.

  3. What is produced when alcohols burn? • Ethanol + oxygen =? • Carbon dioxide and water • Write a balanced equation for this • What is made when Propanol and Butanol are burned. Also write equations for these.

  4. Ethanol reacts with sodium metal • What might be formed? • Does sodium react with oils? What are oils? • Answer –alkanes • So what is different about ethanol when you compare it to ethane? • So what has it reacted with? • Write down your observations when you see the reaction • What is the gas? • Equation – 2C2H5OH + 2Na = 2C2H5ONa + H2 • What happens when you add this compound to water? • Explain your observations

  5. Table 20.5

  6. The alcohols

  7. Propan-1-ol 2-methyl-butanal

  8. 2-methyl-propanoic acid Hexan-3-one

  9. OXIDATIVE PREPARATION OF ALDEHYDES AND KETONES

  10. REMEMBER: • Recall: Alcohols react with oxidising agents • Conversion of an alcohol to an aldehyde or ketone represents an oxidation (removal of H atoms). • Conversion of an aldehyde to a carboxylic acid is also an oxidation (addition of an O atom). • Oxidation can involve the addition of oxygen atoms or it can involve the removal of hydrogen atoms (dehydrogenation).

  11. Oxidations NOTE: A dehydrogenationis also a form of oxidation!

  12. Oxidation of Primary Alcohols The aldehyde can be oxidized in a second step [O] represent an oxidation

  13. Oxidation of Secondary Alcohols

  14. Oxidation of Tertiary Alcohols

  15. Oxidation of Primary Alcohols with KMnO4 You can’t pull the aldehyde out of this reaction, so the only product is the carboxylic acid.

  16. Specifically...

  17. The aldehyde is formed as an intermediate, but it is unstable under the reaction conditions and cannot be isolated. • There is a color change that accompanies the reaction -- the purple solution (KMnO4) changes to a brown mud (MnO2)

  18. Primary alcohols are oxidized by atmospheric oxygen to aldehydes and carboxylic acids. This reaction is very slow. It is catalyzed by enzymes (Acetobacter) This is how wine turns to vinegar!!!

  19. Oxidation of Primary Alcohols to Aldehydes • Requires less vigorous oxidation conditions. • We can try to remove the aldehyde from the reaction medium as quickly as it is formed • Generally, the aldehyde has a lower boiling point than either the corresponding alcohol or carboxylic acid • We can also try to find a milder oxidizing agent.

  20. Dehydrogenation over Copper • This reaction is generally done by passing the vapors of the alcohol through a tube furnace in a stream of inert carrier gas. • This is not a practical laboratory method -- it is better suited to industrial processes. • The reaction stops at the aldehyde stage -- no more removal of hydrogen can take place.

  21. O O K Cr O K Cr O 2 2 7 2 2 7 R C H O H R C O H R C H 2 H SO H SO 2 4 2 4 3+ + Cr Oxidation of Primary Alcohols with K2Cr2O7 • This reaction can also be done using CrO3 (chromic oxide) in sulfuric acid. • The aldehyde is distilled away from the reaction vessel as quickly as it is formed. If the aldehyde is not removed, it will suffer a second oxidation, and the product will be the carboxylic acid.

  22. The acidic conditions keep the chromium in the Cr2O72- state. • Potassium dichromate is not as powerful an oxidizing agent as is potassium permanganate • Sodium dichromate can be substituted for potassium dichromate -- it makes no difference. • There is a color change during the reaction. The orange color of the dichromate changes to the green of Cr3+ ion. • This is not the world’s greatest way to prepare an aldehyde!

  23. Dichromate Oxidation of Ethanol Orange solution Green precipitate

  24. Secondary alcohols are oxidized to ketones Here, it doesn’t really matter whether you use potassium permanganate, potassium dichromate, nitric acid, sodium hypochlorite (Bleach), or other oxidizing agents. Actually, it does matter, but here we are presenting the simple introduction!

  25. What is this called? When would it be used to make acids or aldehydes from primary alcohols Why is it needed to be set up like this? Separating the products

  26. This is how reflux apparatus is set up How is it different to distillation? Why is it important to use this set up with organic molecules? Hint think safety and yield

  27. Chemical tests for Alcohols -OH • What are the two tests that confirm the presence of alcohols? • Which is better? Give reasons 5. Reaction of Alcohol with Phosphorus Penta Chloride (PCl5) When alcohol reacts with phosphorus penta chloride the alkyl chloride is formed. ROH + PCl5  RCl + HCl + POCl3 Alkyl Phosphorus Chloride OxyTrichoride C2H5OH + PCl5  C2H5Cl + HCl + POCl3 Ethyle Chloride

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