Chapter 15 Aldehydes and Ketones Milbank High School

Objectives/Study Questions 1.What is the general structure for an aldehyde? A ketone? 2.How are the common names of aldehydes and ketones determined? How are aldehydes and ketones named using IUPAC nomenclature? 3.Why are the boiling points of aldehydes and ketones higher than those of ethers and alkanes of similar molar masses, but lower than those of comparable alcohols?

Objectives/Study Questions 4.How do the solubilities of aldehydes and ketones of four carbons or less compare to the solubilities of comparable alkanes and alcohols in water? 5.How are aldehydes and ketones prepared? 6.What typical reactions take place with aldehydes and ketones? 7.What are some common aldehydes and ketones and their uses?

Carbonyl Group Carbon atom joined to oxygen by a double bond Ketones                                            Carbon atom joined to oxygen by a double bond Ketones Aldehydes             

Aldehydes Comes from alcohol dehydrogenation Obtained by removing of a hydrogen from an alcohol                                                       

Aldehydes Both common and IUPAC names frequently used Common names from acids from which aldehydes can be converted                                                            

Aldehydes IUPAC Longest chain with aldehyde Drop “e” and add “-al” Aldehyde takes precedence over all other groups so far Examples

Ketones Naming: Drop “e”, add “-one” Many common names                                                                        Naming: Drop “e”, add “-one” Many common names Simplest is 3 carbons C. name: acetone IUPAC: propanone

Ketones Carbonyl carbon gets lowest number See examples…

Common Carbonyl Compounds Formaldehyde Manufactured from methanol Used in many polymers Acetaldehyde Prepared from ethyl alcohol Formed in the detoxification of alcohol in the liver Acetone Formed in the human body as a by-product of lipid metabolism Excreted in the urine Hormones Steroid hormones Progesterone/Testosterone

Physical Properties of Aldehydes and Ketones Carbon-oxygen double bond is very polar Affects boiling points More than ethers (C-O bonds) Less than alcohols (C-OH bonds) Odors Low aldehydes very pungent High aldehydes pleasant odors (perfumes) Solubility Similar to alcohols and ethers Soluble up to about 4 carbons Insoluble after that

Preparation of Aldehydes Oxidation Leads to carboxylic acid unless care is taken 1° alcohols                                                                                                                               

Preparation of Ketones Oxidation of a 2° alcohol Utilizes chromium compounds and sulfuric acid                                                                

Chemical Properties of Aldehydes and Ketones Both under-go combustion reactions Oxidation Aldehydes can be oxidized, ketones can’t See Pg 403 Tollen’s reagent Benedict’s reagent Fehling’s reagent  

Chemical Properties of Aldehydes and Ketones                                              Chemical Properties of Aldehydes and Ketones Reduction Variety of agents can reduce aldehydes and ketones to alcohols NaBH4 and H2 commonly used                                                                                                       

Chemical Properties of Aldehydes and Ketones Hydration Formaldehyde dissolves readily in water Acetaldehyde somewhat also Form hydrates                                                                              

Chemical Properties of Aldehydes and Ketones                                                                                 Chemical Properties of Aldehydes and Ketones Addition of Alcohols to Carbonyl Groups Hemiacetal Aldehyde + alcohol Hemiketal Ketone + alcohol Not very stable Differs from 1 mol to 2 mol

Chemical Properties of Aldehydes and Ketones Hemiacetals + HCl = acetal Hemiketal + HCl = ketal