dr.fatma mahfouz mohamed saleh

استاذ الكيمياء العضوية المساعد

غديرالفايز- علوم

 

 

 


Naming Alcohols

Alcohols contain anOH group attached to a saturated carbon. The common names for alcohols are based on the name of the alkyl group.

 

 

CH3OH

 

Methyl alcohol

 

CH3CH2OH

 

Ethyl alcohol

 

CH3CHOHCH3

 

Isopropyl alcohol


The systematic nomenclature for alcohols adds the ending -ol to the name of the parent alkane and uses a number to identify the carbon that carries the OH group. The systematic name for isopropyl alcohol, for example, is 2-propanol.

 

 

CH3OH

 

Methanol

 

CH3CH2OH

 

Ethanol

 

CH3CHOHCH3

 

2-Propanol


 


Methanol, or methyl alcohol, is also known as wood alcohol because it was originally made by heating wood until a liquid distilled. Methanol is highly toxic, and many people have become blind or died from drinking it. Ethanol, or ethyl alcohol, is the alcohol associated with "alcoholic" beverages. It has been made for at least 6000 years by adding yeast to solutions that are rich in either sugars or starches. The yeast cells obtain energy from enzyme-catalyzed reactions that convert sugar or starch to ethanol and CO2.

C6H12O6(aq) 2 CH3CH2OH(aq) + 2 CO2(g)

When the alcohol reaches a concentration of 10 to 12% by volume, the yeast cells die. Brandy, rum, gin, and the various whiskeys that have a higher concentration of alcohol are prepared by distilling the alcohol produced by this fermentation reaction. Ethanol isn't as toxic as methanol, but it is still dangerous. Most people are intoxicated at blood alcohol levels of about 0.1 gram per 100 mL. An increase in the level of alcohol in the blood to between 0.4 and 0.6 g/100 mL can lead to coma or death.

 

 

 

 

 

 


Testing Blood Alcohol Levels

The method of choice for determining whether an individual is DUIdriving under the influence or DWI driving while intoxicated  is the Breathalyzer, for which a patent was issued to R. F. Borkenstein in 1958. The chemistry behind the Breathalyzer is based on the reaction between alcohol in the breath and the chromate or dichromate ion.

3 CH3CH2OH(g) + 2 Cr2O72-(aq) + 16 H+(aq) 3 CH3CO2H(aq) + 4 Cr3+(aq) + 11 H2O(l)

The instrument contains two ampules that hold small samples of potassium dichromate dissolved in sulfuric acid. One of these ampules is used a reference. The other is opened and the breath sample to be analyzed is added to this ampule. If alcohol is present in the breath, it reduces the yellow-orange Cr2O72- ion to the green Cr3+ ion. The extent to which the color balance between the two ampules is disturbed is a direct measure of the amount of alcohol in the breath sample. Measurements of the alcohol on the breath are then converted into estimates of the concentration of the alcohol in the blood by assuming that 2100 mL of air exhaled from the lungs contains the same amount of alcohol as 1 mL of blood.

Measurements taken with the Breathalyzer are reported in units of percent blood-alcohol concentration (BAC). In most states, a BAC of 0.10% is sufficient for a DUI or DWI conviction. (This corresponds to a blood-alcohol concentration of 0.10 grams of alcohol per 100 mL of blood.)

Ethanol is oxidized to CO2 and H2O by the alcohol dehydrogenase enzymes in the body. This reaction gives off 30 kilojoules per gram, which makes ethanol a better source of energy than carbohydrates (17 kJ/g), and almost as good a source of energy as fat (38 kJ/g). An ounce of 80-proof liquor can provide as much as 3% of the average daily caloric intake, and drinking alcohol can contribute to obesity. Many alcoholics are malnourished, however, because of the absence of vitamins in the calories they obtain from alcoholic beverages.

 

 

 

Solubilities of Alcohols


As a general rule, polar or ionic substances dissolve in polar solvents; nonpolar substances dissolve in nonpolar solvents. As a result, hydrocarbons don't dissolve in water. They are often said to be immiscible (literally, "not mixable") in water. Alcohols, as might be expected, have properties between the extremes of hydrocarbons and water. When the hydrocarbon chain is short, the alcohol is soluble in water. There is no limit on the amount of methanol (CH3OH) and ethanol (CH3CH2OH), for example, that can dissolve in a given quantity of water. As the hydrocarbon chain becomes longer, the alcohol becomes less soluble in water, as shown in the table below. One end of the alcohol molecules has so much nonpolar character it is said to be hydrophobic (literally, "water-hating"). The other end contains an -OH group that can form hydrogen bonds to neighboring water molecules and is therefore said to be hydrophilic (literally, "water-loving"). As the hydrocarbon chain becomes longer, the hydrophobic character of the molecule increases, and the solubility of the alcohol in water gradually decreases until it becomes essentially insoluble in water.

Solubilities of Alcohols in Water

 

 

Formula


Name


Solubility in
Water (g/100 g)

 

CH3OH


methanol


infinitely soluble

 

CH3CH2OH


ethanol


infinitely soluble

 

CH3(CH2)2OH


propanol


infinitely soluble

 

CH3(CH2)3OH


butanol


9

 

CH3(CH2)4OH


pentanol


2.7

 

CH3(CH2)5OH


hexanol


0.6

 

CH3(CH2)6OH


heptanol


0.18

 

CH3(CH2)7OH


octanol


0.054

 

CH3(CH2)9OH


decanol


insoluble in water

 

 

 


Primary, Secondary, and Tertiary Alcohols

Alcohols are classified as either primary (1), secondary (2), or tertiary (3) on the basis of their structures.

 

Ethanol is a primary alcohol because there is only one alkyl group attached to the carbon that carries the OH substituent. The structure of a primary alcohol can be abbreviated as RCH2OH, where R stands for an alkyl group. The isopropyl alcohol found in rubbing alcohol is a secondary alcohol, which has two alkyl groups on the carbon atom with the OH substituent (R2CHOH). An example of a tertiary alcohol (R3COH) is tert-butyl (or t-butyl) alcohol or 2-methyl-2-propanol.

 

 

 


Phenols

Another class of alcohols are the phenols, in which an OH group is attached to an aromatic ring, as shown in the figure below. Phenols are potent disinfectants. When antiseptic techniques were first introduced in the 1860s by Joseph Lister, it was phenol (or carbolic acid, as it was then known) that was used. Phenol derivatives, such as o-phenylphenol, are still used in commercial disinfectants such as Lysol.

 

 

 

 


Boiling Points of Alcohols

Water has an unusually high boiling point because of the hydrogen bonds between the H2O molecules. Alcohols can form similar hydrogen bonds, as shown in the figure below.

 

As a result, alcohols have boiling points that are much higher than alkanes with similar molecular weights. The boiling point of ethanol, for example, is 78.5ºC, whereas propane, with about the same molecular weight, boils at -42.1ºC.

 

 

 


Alcohols as Acids and Bases

Alcohols are Bronsted acids in aqueous solution.

CH3CH2OH(aq) + H2O(l) H3O+(aq) + CH3CH2O-(aq)

Alcohols therefore react with sodium metal to produce sodium salts of the corresponding conjugate base.

2 Na(s) + 2 CH3OH(l) 2 Na+(alc) + 2 CH3O-(alc) + H2(g)

The conjugate base of an alcohol is known as an alkoxide.

 

 

[Na+][CH3O-]

 

[Na+][CH3CH2O-]

 

sodium methoxide

 

sodium ethoxide

 

 

Preparation of Alcohols

Alcohols can be prepared by adding water to an alkene in the presence of a strong acid such as concentrated sulfuric acid. This reaction involves adding an H2O molecule across a C=C double bond. Because these reactions follow Markovnikov's rule , the product of the reaction is often a highly substituted 2 or 3 alcohol.

 

Less substituted 1 alcohols can be prepared by substitution reactions that occur when a primary alkyl halide is allowed to react with the OH- ion.

CH3CH2CH2Br + OH-  CH3CH2CH2OH + Br -

 

 

 

 

Ethers

Alcohols (ROH) can be thought of as derivatives of water in which one of the hydrogen atoms has been replaced by an alkyl group. If both of the hydrogen atoms are replaced by alkyl groups, we get an ether (ROR). These compounds are named by adding the word ether to the names of the alkyl groups.

 

 

CH3CH2OCH2CH3

 


diethyl ether


Diethyl ether, often known by the generic name "ether," was once used extensively as an anesthetic. Because mixtures of diethyl ether and air explode in the presence of a spark, ether has been replaced by safer anesthetics.

 

 

 

 

 


Alcohols versus Ethers

There are important differences between both the physical and chemical properties of alcohols and ethers. Consider diethyl ether and 1-butanol, for example, which are constitutional isomers with the formula C4H10O.

 

 

CH3CH2OCH2CH3

 


CH3CH2CH2CH2OH

 

BP = 34.5ºC

 


BP = 117.2ºC

 

d = 0.7138 g/mL

 


d = 0.8098 g/mL

 

insoluble in water

 


soluble in water


The shapes of these molecules are remarkably similar, as shown in the figure below.

 

The fundamental difference between these compounds is the presence of OH groups in the alcohol that are missing in the ether. Because hydrogen bonds can't form between the molecules in the ether, the boiling point of this compound is more than 80ºC lower than the corresponding alcohol. Because there are no hydrogen bonds to organize the structure of the liquid, the ether is significantly less dense than the corresponding alcohol.

Ethers can act as a hydrogen-bond acceptor, as shown in the figure below. But, they can't act as hydrogen-bond donors. As a result, ethers are less likely to be soluble in water than the alcohol with the same molecular weight.

 

The absence of an OH group in an ether also has important consequences for its chemical properties. Unlike alcohols, ethers are essentially inert to chemical reactions. They don't react with most oxidizing or reducing agents, and they are stable to most acids and bases, except at high temperatures. They are therefore frequently used as solvents for chemical reactions.

Compounds that are potential sources of an H+ ion, or proton, are often described as being protic. Ethanol, for example, is a protic solvent.

CH3CH2OH(aq) + H2O(l) H3O+(aq) + CH3CH2O-(aq)

Substances that can't act as a source of a proton are said to be aprotic. Because they don't contain an OH group, ethers are aprotic solvents.

Ethers can be synthesized by splitting out a molecule of water between two alcohols in the presence of heat and concentrated sulfuric acid.

 

 

 

H+

 

 


2 CH3CH2OH

 

CH3CH2OCH2CH3

 

They can also be formed by reacting a primary alkyl halide with an alkoxide ion.

CH3CH2CH2Br + CH3O- CH3CH2CH2OCH3 + Br-

 

 

 

 

 

 

By .. Ghadeer Othman Al.Fayez

 


Thanks for your time

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 رد

الساعات المكتبية

لطالبات كلية التربية

السبت - المحاضرة الرابعةمن 11 الي المحاضرة السادسة  1,50

الاثنين - المحاضرة الثانية من 9 الي المحاضرة الرابعة 11

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