All aldehydes and ketones are soluble in organic solvents and, in general, are less dense than water. Similar to the other oxygen-containing functional groups discussed thus far, aldehydes and ketones are also widespread in nature and are often combined with other functional groups.
Examples of naturally occurring molecules which contain a aldehyde or ketone functional group are shown in the following two figures. The compounds in the figure 9.
Many of these molecular structures are chiral and have distinct stereochemistry. When chiral compounds are found in nature they are usually enantiomerically pure, although different sources may yield different enantiomers.
For example, carvone is found as its levorotatory R -enantiomer in spearmint oil, whereas, caraway seeds contain the dextrorotatory S -enantiomer. In this case the change of the stereochemistry causes a drastic change in the perceived scent. Aldehydes and ketones are known for their sweet and sometimes pungent odors. The odor from vanilla extract comes from the molecule vanillin. Likewise, benzaldehyde provides a strong scent of almonds.
Because of their pleasant fragrances aldehyde and ketone containing molecules are often found in perfumes. However, not all of the fragrances are pleasing. In particular, 2-Heptanone provides part of the sharp scent from blue cheese and R -Muscone is part of the musky smell from the Himalayan musk deer.
Lastly, ketones show up in many important hormones such as progesterone a female sex hormone and testosterone a male sex hormone. Notice how subtle differences in structure can cause drastic changes in biological activity. The ketone functionality also shows up in the anti-inflammatory steroid, Cortisone.
Ketones are formed in the human body as a by-product of lipid metabolism. Acetone is also produced as a breakdown product of acetoacetic acid. Acetone can then be excreted from the body through the urine or as a volatile product through the lungs.
Normally, ketones are not released into the bloodstream in appreciable amounts. Instead, ketones that are produced during lipid metabolism inside cells are usually fully oxidized and broken down to carbon dioxide and water.
This is because glucose is the primary energy source for the body, especially for the brain. Glucose is released in controlled amounts into the bloodstream by the liver, where it travels throughout the body to provide energy. For the brain, this is the primary energy source, as the blood-brain barrier blocks the transport of large lipid molecules.
However, during times of starvation, when glucose is unavailable, or in certain disease states where glucose metabolism is disregulated, like uncontrolled diabetes mellitus, the ketone concentrations within blood rises to higher levels to provide an alternative energy source for the brain. Ketoacidosis can be a life threatening event. Ketones can be easily detected, as acetone is excreted in the urine. In severe cases, the odor of acetone can also be noted on the breath. Carboxylic Acids can be easily recognized as they have a carbonyl carbon that is also linked directly to an alcohol functional group.
So the carbonyl carbon is also attached directly to an alcohol. In the ester functional group, the carbonyl carbon is also directly attached as part of an ether functional group. Carboxylic acids are organic compounds which incorporate a carboxyl functional group, CO 2 H. The name carboxyl comes from the fact that a carbonyl and a hydroxyl group are attached to the same carbon. Carboxylic acids are named such because they can donate a hydrogen to produce a carboxylate ion.
The factors which affect the acidity of carboxylic acids will be discussed later. An ester is an organic compound that is a derivative of a carboxylic acid in which the hydrogen atom of the hydroxyl group has been replaced with an alkyl group.
The general formula for an ester is shown below. The R group can either be a hydrogen or a carbon chain. The steps for naming esters along with two examples are shown below. Carboxylic acids can form hydrogen bond dimers which increases their boiling points above that of alcohols of similar size Table 9.
Small esters have boiling points which are lower than those of aldehydes and ketones with similar mass Table 9. Esters, like aldehydes and ketones, are polar molecules. Thus, their boiling points are higher than ethers and lower than aldehydes and ketones of similar size. Low molecular weight carboxylic acids tend to be liquids at room temperature, whereas larger molecules form waxy solids.
Carboxylic acids that range in carbon chain length from 12 carbons are typically called fatty acids, as they are commonly found in fats and oils. Comparable to other oxygen containing molecules, the short-chain carboxylic acids tend to be soluble in water, due to their ability to form hydrogen bonds.
As the carbon chain length increases, the solubility of the carboxylic acid in water goes down. Esters can also hydrogen bond with water, although not as efficiently as carboxylic acids, and thus they are slightly less soluble in water than carboxylic acids of similar size. Carboxylic acids typically have in unpleasant, pungent and even rancid odors. The smell of vinegar, for example, is due to ethanoic acid also known as acetic acid. The odor of gyms and unwashed socks is largely caused by butanoic acid, and hexanoic acid is responsible for the strong odor of limburger cheese.
Due to their acidic nature, carboxylic acids also have a sour taste as noted for vinegar and the citric acid found in many fruits. Esters, on the otherhand, have enjoyable aromas and are responsible for the aroma of many fruits and flowers. Esters can also have fruity flavors. Carboxylic acids and esters are common in nature and are used for a multitude of purposes. For example, ants in the Formicidae family use the simplest carboxylic acid, formic acid, as both a chemical defense and as an attack to subdue prey Figure 9.
Acetic acid also gives sourdough bread its sharp taste and accounts for the sour flavors in wine. Citric acid is found in many fruits and accounts for their sour flavor. Other carboxylic acids such as PABA and glycolic acid are used in the cosmetic industry. PABA which is produced by plants, fungi, and bacteria is a common component of food and is related in structure to the vitamin folate.
In PABA was patented as one of the first compounds used in the manufacture of sunscreen. However, its use has fallen out of favor since the mids due to concerns that it may increase cellular UV damage, as well as contribute to allergies. In food processing it is used as a preservative and in the skin care industry it is used most often as a chemical peel to reduce facial scarring by acne. A Formic acid is the defense toxin used by ants in the Formicidae family.
The photo on the left shows various flavors of vinegar at a market in France. Photo by Georges Seguin C Citric acid is a common component of fruit, providing a sour taste. It was patented in for its use in sunscreen products. However, due to safety concerns and allergic response, the use of PABA has been discontinued for this purpose. Suncreen photo provided by HYanWong E Glycolic acid is commonly used in cosmetics as a chemical peel used to reduce scarring by acne.
Glycolic study provided by Jaishree Sharad. Esters are readily synthesized and naturally abundant contributing to the flavors and aromas in many fruits and flowers. For example, the ester, methyl salicylate is also known as the oil of wintergreen Figure 9. The fruity aroma of pineapples, pears and strawberries are caused by esters, as well as the sweet aroma of rum.
Esters also make up the bulk of animal fats and vegetable oils as triglycerides. The formation of lipids and fats will be described in more detail in Chapter Alcohol functional groups can be involved in several different types of reactions.
In this section, we will discuss two major types of reactions. The first are the dehydration reactions and the second are the oxidation reactions. Alcohols can also be involved in addition and substitution reactions with other functional groups like aldehydes, ketones, and carboxylic acids. These types of reactions will be discussed in more detail within the aldehyde and ketone, and carboxylic acid sections.
In chapter 8, we learned that alcohols can be formed from the hydration of alkenes during addition reactions. We also learned that the opposite reaction can also occur. Alcohols can be removed or eliminated from molecules through the process of dehydration or the removal of water.
The result of the elimination reaction is the creation of an alkene and a molecule of water. Elimination reactions that occur with more complex molecules can result in more than one possible product.
In these cases, the alkene will form at the more substituted position at the carbon that has more carbon atoms and less hydrogen atoms attached to it. For example, in the reaction below, the alcohol is not symmetrical. Thus, there are two possible products of the elimination reaction, option 1 and option 2.
In option 1, the alkene is formed with the carbon that has the fewest hydrogens attached, whereas in option 2 the alkene is formed with the carbon that has the most hydrogens attached. Thus, option 1 will be the major product of the reaction and option 2 will be the minor product. Alcohol elimination reactions using small 1 o alcohols can also be used to produce ethers.
To produce an ether rather than the alkene, the temperature of the reaction must be reduced and the reaction must be done with excess alcohol in the reaction mixture. For example:. In this reaction alcohol has to be used in excess and the temperature has to be maintained around K. If alcohol is not used in excess or the temperature is higher, the alcohol will preferably undergo dehydration to yield alkene.
The dehydration of secondary and tertiary alcohols to get corresponding ethers is unsuccessful as alkenes are formed too easily in these reactions. Some alcohols can also undergo oxidation reactions. Remember in redox reactions, the component of the reaction that is being oxidized is losing electrons LEO while the molecule receiving the electrons is being reduced GER.
In organic reactions, the flow of the electrons usually follows the flow of the hydrogen atoms. Thus, the molecule losing hydrogens is typically also losing electrons and is the oxidized component. Supplier Information. Read full article at Wikipedia. Average Mass.
Monoisotopic Mass. Metabolite of Species. Mus musculus NCBI:txid Saccharomyces cerevisiae NCBI:txid Source: yeast. Escherichia coli NCBI:txid The stems for the common names of the first four aldehydes are as follows: 1 carbon atom: form - 2 carbon atoms: acet - 3 carbon atoms: propion - 4 carbon atoms: butyr -. Give the common name for each ketone. There is a chlorine Cl atom on the seventh carbon atom; numbering from the carbonyl group and counting the carbonyl carbon atom as C1, we place the Cl atom on the seventh carbon atom.
Exercise Draw the structure for each compound. Summary The common names of aldehydes are taken from the names of the corresponding carboxylic acids: formaldehyde, acetaldehyde, and so on.
Exercises Name each compound. Name each compound. Consumers may be exposed to acetaldehyde in cheese, heated milk, cooked beef, cooked chicken, and rum. It is an important component of food flavourings in low concentrations which are generally recognised as safe and is added to milk products, baked goods, fruit juices, sweets, desserts, and soft drinks.
It is an especially useful for imparting orange, apple, and butter flavours. It is used in the manufacture of vinegar and yeast and as a fruit and fish preservative. Consumers may have been exposed to acetaldehyde in room air deodorisers.
Exposure in the home environment may occur from the products of burning wood in stoves or fire places. Skip to main content. Acetaldehyde Overview Health effects Environmental effects Sources of emissions References Overview Acetaldehyde is primarily used as an intermediate in the manufacture of a range of chemicals, perfumes, aniline dyes, plastics and synthetic rubber and in some fuel compounds.
Physical properties Clear colourless fuming liquid with a pungent, fruity odour. Specific Gravity: 0. Chemical properties This chemical is dangerous when exposed to heat or flame. Australia's acetaldehyde emission report. Description Acetaldehyde is an irritant of the skin, eyes, mucous membranes, throat and respiratory tract. Acetaldehyde is a substance which may reasonably be anticipated to be a carcinogen.
Entering the body Exposure to acetaldehyde is primarily through breathing though skin absorption and ingestion are also possible. Exposure Principal human exposure will be from inhalation of ambient air from urban areas or near sources of combustion. Drinking water guidelines There is no guideline for acetaldehyde in the Australian Drinking Water Guidelines. Environmental effects In sufficient concentrations acetaldehyde can effect animals in a similar way to humans.
Entering the environment Because acetaldehyde rapidly evaporates it most likely to be transported in air though it degrades rapidly and is therefore unlikely to be transported far. Where it ends up It will rapidly evaporate from water or land.
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