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WEEK 8
ALCOHOLS AND ETHERS
Alcohols are the first class of organic compounds that function as both disinfectant and
preservative agents. Ethers are considered to be derivatives of alcohols.
ALCOHOLS
Alcohols are organic compounds containing one or more –OH groups. The alcohols may
be considered as derivatives of the hydrocarbons in which one or more hydrogen atoms
are replaced by –OH groups. Alcohols may be classified according to the number of
–OH groups they contain.
MONOHYDROXY ALCOHOLS – Alcohols containing only one –OH group are
called MONOHYDROXY ALCOHOLS. The simplest monohydroxy alcohol is methyl
alcohol.
H
H
C OH
H
alcohol
methyl
In methyl alcohol, one of the hydrogen atoms in methane (CH4) has been replaced by the
–OH group. Another way to name this alcohol would be to take the name of the
corresponding alkane, remove the –e and add –ol. Therefore another name for methyl
alcohol would be methanol. The next member of the series is ethyl alcohol or ethanol.
H
H
H
C
C OH
H
H
Monohydroxy alcohols are further classified according to the place of attachment of the –
OH group as primary, secondary, or tertiary.
PRIMARY ALCOHOLS
These are alcohols in which the hydroxyl group is attached to a carbon atom that is joined
to only one other carbon atom. For example:
H
H C
H
H
H
H
C C
C OH
H
H
H
n-Butyl alcohol (butanol)
This is a primary alcohols because the carbon to which the –OH group is attached is also
joined to two hydrogen atoms but only one other carbon atom.
SECONDARY ALCOHOLS
These are alcohols in which the hydroxyl group is attached to a carbon atom that is joined
to two other carbon atoms. For example:
H
H
H
H
H
C
C
C
C H
H
H
OH H
Secondary butyl alcohol
The carbon to which the –OH group is attached is also joined to one hydrogen atom and
two other carbon atoms.
TERTIARY ALCOHOLS
These are alcohols in which the hydroxyl group is attached to a carbon atom that is joined
to three other carbon atoms.
H
H
H
H C
C
C
H
H C
H
OH
H
H
Tertiary butyl alcohol
It is not possible to have a quaternary alcohol because that would mean that there would
be a total of 5 bonds on the carbon atom.
DIHYDROXY ALCOHOLS
These are alcohols containing two –OH groups. They are also sometimes known as
GLYCOLS. An example is ethylene glycol:
H
H C
H
C H
HO OH
Ethylene glycol is named as an alkene even though it does not have a double bond. It is
named this way because it is synthesized from ethylene (CH2 CH2) . Because of its
high boiling point, low freezing point, and high solubility in water, ethylene glycol is
used commercially as a coolant/antifreeze for automobile engines. IN EMBALMING
FLUIDS, GLYCOLS REPRESENT THE SIMPLEST CLASS OF HUMECTANTS OR
MOISTURE- RETAINING AGENTS.
TRIHYDROXY ALCOHOLS
These include alcohols containing three –OH groups. The most common of these is
glycerin (glycerol). GLYCERIN IS USED AS BOTH A HUMECTANT AND A
SOLVENT IN EMBALMING FLUID.
POLYHYDROXY ALCOHOLS
Alcohols containing more than three –OH groups are included in this category.
SORBITOL, MANITOL AND DULCITOL, ARE COMMONLY EMPLOYED IN
EMBALMING FLUIDS AS HUMECTANTS.
IMPORTANT ALCOHOLS IN EMBALMING
Methyl alcohol (methanol), the first member of the series of primary monohydroxy
alcohols, is also known as Wood alcohol because it is produced by a process known as
the destructive distillation of wood. Destructive distillation involves heating an organic
substance(in this case wood) in the absence of air or oxygen and condensing the resulting
vapors. It is extremely important to exclude the oxygen, because the complete oxidation
of any organic substance results in the production of carbon dioxide and water. Once
methanol has been formed, it can undergo moderate or partial oxidation. For example:
partial
partial
alcohol oxidation aldehyde oxidation
acid
As a result methyl alcohol is instrumental in the commercial production of formaldehyde
(methanol
methanal).
During complete oxidation of methyl alcohol it burns with a blue flame, forming carbon
dioxide and water.
2CH3OH + 3O2
2CO2 + 4H2O
If only partial oxidation of methyl alcohol occurs formaldehyde is produced:
2CH3OH + O2
Cu
2HCHO + 2H2O
This process of partial oxidation explains the toxicity of methyl alcohol. If someone
were to ingest methyl alcohol, the methyl alcohol is partially oxidized to formaldehyde in
the body.
Ethyl alcohol is the second member of the series of primary monohydroxy alcohols.
Ethanol is also called grain alcohol because it is produced by the fermentation of
carbohydrates.
C6H12O6
zymase
carbohydrate
2C2H5OH + 2CO2
ethanol
Like methanol, ethanol burns with a blue flame, forming carbon dioxide and water
(complete oxidation).
2CO2 + 3H2O
C2H5OH + 3O2
Partial oxidation produces acetaldehyde (ethanal).
2C2H5OH + O2
2CH3CHO + 2H2O
ethanal
The oxidation and reduction of primary alcohols may be summarized by the following
diagram:
Oxidation
Alcohol
Aldehyde
Acid
CO2
+
H 2O
Reduction
Denatured alcohol is ordinary ethyl alcohol to which poisonous or ill-tasting substances
have been added in order to render it unfit for use as a beverage. In this form, it can be
used in industry. Specially purified methyl and ethyl alcohols that are free from water
and other impurities are called Absolute alcohol.
The third member of the series of primary, monohydroxy alcohols is propanol. Like its
predecessors, n-propyl alcohol undergoes oxidation and reduction patterns typical of all
the primary alcohols. However, its isomer (isopropyl alcohol) is of special interest.
Isopropyl alcohol (rubbing alcohol) is a secondary alcohol.
H
H
H
H
C
C
C
H
H
OH H
Isopropyl alcohol
Secondary alcohols, on partial oxidation, yield ketones:
H
H
H
H
C
C
C
H
OH H
Isopropyl alcohol
H
+ 1/2 O2
H
H
H
H
C
C
C H + H2O
H
O
ketone
H
Isopropyl alcohol has many industrial uses, because it is relatively inexpensive and is
sold tax free without restriction. Little use is made of it in embalming fluid. It is an
excellent disinfectant, possessing approximately twice the germicidal strength of ethyl
alcohol.
The following table summarizes the important alcohols utilized in the embalming
process.
__________________________________
NAME
FUNCTION
Methyl alcohol
Solvent
Lowers the freezing point of the fluid
Formaldehyde antipolymerant
Ethyl alcohol
Solvent
Lowers the freezing point of the fluid
Preservative
Disinfectant
Isopropyl alcohol
Disinfectant
Ethylene glycol
Humectant
Glycerin
Humectant
Solvent
Lubricant
Penetrating agent
Increases the effectiveness of germicides
in solution
PHENOLS
Phenols are derivatives of benzene containing one or more –OH groups.
OH
= C6H5OH = Carbolic acid
Phenol
Phenols are colorless, crystalline solids that are soluble in water and weakly acidic (pH
6). Phenol’s other name is Carbolic acid. A number of disinfectant compounds are
derived from phenol, the most advertised of which is Listerine. Phenol has been used as
a general disinfectant. It has also been used in compounds that are used to deodorize
sewage.
CRESOLS
Phenols that are derivatives of toluene are called cresols. There are three isomers:
OH
OH
OH
CH3
CH3
CH3
Ortho-cresol
Meta-cresol
Para-cresol
A mixture of the three is known as tricresol. The cresols have a greater germicidal power
than phenol and are somewhat less toxic to humans. Cresols are combined with soap to
produce Lysol. One of the highly desirable qualities of a good disinfectant is the ability
to work well in the presence of organic matter such as soap. Because many phenolic
derivatives possess this quality, they are extensively used in embalming procedures.
COMPARISON OF ALCOHOLS AS GERMICIDES
Concentration is the most critical factor in considering the disinfectant or preservative
action of any of the previously discussed compounds. Ethyl alcohol is most effective as a
disinfectant in concentrations of 50% to 70%. In concentrations exceeding 70%, ethanol
is actually less effective, because its high affinity for water impedes its ability to
penetrate cell membranes at these levels. By way of contrast, glycerin exhibits its best
antiseptic qualities in strong solutions. In weak ones, it will actually promote the growth
of bacteria.
The use of phenol as a disinfectant varies widely according to its concentrations. In
solutions containing 5% phenol, the material has the physical appearance of a reddishpurple liquid and the chemical characteristic of extreme causticity to living tissues.
Although it must be handled with protective gloves, it is valuable in bleaching
discolorations and also may be used in reducing swollen areas in human remains. This
concentration of phenol is available in a number of commercial preparations and either
may be applied by external pack or injected directly into the affected area by hypodermic
syringe. When the concentration is reduced to 3%, the solution becomes somewhat less
caustic and yet is still effective as an external drying agent. Lowering the concentration
to 2% produces a disinfectant that is routinely applied to laboratory tabletops in
microbiology labs. Gloves are not necessary at this concentration. At a 1%
concentration, it is used in mouthwash (Listerine). The actual compound that you will
find listed is Thymol and not phenol. Thymol is a derivative of phenol:
OH
CH3
CH
CH3
H3C
Thymol
This compound demonstrates a pattern that will consistently recur throughout organic
chemistry. THE SIMPLEST ORGANIC SUBSTANCES APPEAR TO BE THE MOST
CAUSTIC. When the basic substance is modifids either by the addition of carbons in the
chain or the substitution of side chains on the essential structure, its caustic or astringent
characteristic is substantially reduced without the loss of germicidal activity. In fact, the
germicidal quality seems to increase. For example, formaldehyde is the smallest
aldehyde and also the most astringent.
THIOALCOHOLS (MERCAPTANS)
Mercaptans are the sulfur analogs of alcohols. These compounds contain the sulfhydryl
group, -SH, instead of the hydroxyl group, -OH. The general formula for thioalcohols is
R-SH. An example of a mercaptan is ethyl mercaptan: CH3CH2SH.
The presence of sulfur produces obnoxious odors. Ethyl mercaptan is a tracer substance
added to natural gas (which is odorless) in order to make gas leaks more readily
detectable. The compound responsible for skunk odor is also a mercaptan. The odor of
burning flesh and hair is due to the fact that many proteins are rich in sulhydryl groups.
ETHERS
Ethers are compounds in which two alkyl groups are attached to an oxygen atom. Ethers
may be viewed as derivatives of alcohols in which the H of the ROH has been replaced
with an alkyl group to form a substance with the general formula ROR. They also may
be considered as derivatives of water in which both hydrogen atoms have been replace by
alkyl groups. An additional expression of the general formula is ROR’, where R’ may or
may not be identical with R. It is important to note that each R group must contain a
minimum of a methyl (-CH3) group.
SIMPLE ETHERS
In simple ethers, the two alkyl groups are identical. These compounds are named by
using the name of the alkyl groups attached to the oxygen. For example:
H
H
C
H
O
C H
H
H
dimethyl ether
This substance may also be called methyl ether. The next member of the series would be:
H H
H
H
C C O C C
H
H H
H
H
H
This compound is diethyl ether or ethyl ether. Under its common name, ether, this
substance has become widely known for its qualities as a surgical anesthetic. It is no
longer used this way because it is highly flammable and has undesirable side effects,
including nausea, vomiting, and irritation of the respiratory passages.
The simple ethers are chemically inert, so they make excellent solvents for organic
compounds. As a result, they have sometimes been incorporated in embalming fluids for
this purpose. However, because they are highly flammable, a great deal of care must be
exercised in their use.
MIXED ETHERS
In mixed ethers, the two alkyl groups are different; hence their other name of
unsymmetrical ethers. These are also named according to their alkyl groups. For
example:
H
H
H
H
C O
C
C
H
H
H
H
Ethyl methyl ether
WEEK 8
ALDEHYDES AND KETONES
ALDEHYDES
As a group, aldehydes comprise the largest percentage of disinfectant-preservative
chemical agents routinely incorporated into embalming fluids. Aldehydes are organic
compounds containing one or more –CHO groups. They are considered to be derivatives
of the hydrocarbons in which two hydrogen atoms on the same carbon atom have been
replaced by an oxygen atom. For example:
O
H
H
C
H
H
C
H
H
Hydrocarbon
Aldehyde
In naming the aldehydes, the –e ending of the corresponding hydrocarbon is changed to –
al. Thus:



Methane – methanal
Ethane – ethanal
Propane – propanal
This naming system also reflects the relationship of an aldehyde to the alcohol from
which it can be formed. We have previously defined oxidation as the removal of
hydrogen. Oxidation of methanol yields methanal. Similarly, ethanal is formed from
ethanol and propanal from propanol. The name aldehyde is an acronym for the first
syllables of the three words alcohol deprived of hydrogen. Aldehydes can also be named
according to their corresponding acids. Remember that a reduction of an organic acid
produces an aldehyde.
For example, the first member of the aldehyde series named according to the first naming
system is methanal (HCHO). Formaldehyde is the familiar name for this substance.
According to its derivation, then, formaldehyde is named as the reduction production of
formic acid. Formic acid comes from ants (Latin formica, meaning ant). Formic acid
was originally obtained by distilling ants. Formaldehyde is the primary preservative in
arterial embalming fluids.
FORMALDEHYDE (Methanal)
Formulas:
O
CH2O
HCHO
H
C H
The commercial method of preparation of formaldehyde is the partial oxidation of methyl
alcohol, accomplished by passing methyl alcohol vapors over sheets of hot copper that
act as a catalyst. The equation is:
2CH3OH + O2
Cu
2HCHO + 2H2O
Remember that if we were to completely oxidize methanol, we would get carbon dioxide
and water.
PROPERTIES OF FORMALDEHYDE
1. It is a colorless gas with an irritating odor. Formaldehyde is highly dehydrating
and has been shown to have a detrimental effect on the nasal and pharyngeal
mucous membranes.
2. It is quite soluble in water. Formaldehyde is generally available as formalin, an
aqueous solution containing 37% formaldehyde gas by mass of 40% by volume.
In order to increase the concentration above this level, it is necessary to use an
additional solvent such as ethyl alcohol. Another way to express the
concentration of formaldehyde in embalming fluids is INDEX. Index is defined
as the number of grams of pure formaldehyde gas dissolved in 100 milliliters of
solution.
3. Formaldehyde combines with water, forming methylene glycol:
CH2O + HOH
CH2(OH)2
When in solution in water, most of the formaldehyde is actually in the form of
methylene glycol.
4. It polymerizes to form paraformaldehyde. Polymerization is a reaction between
molecules of the same kind that produces a substance having a molecular mass
that is approximately a multiple of the original substance. A polymer is the
product resulting from polymerization. When formaldehyde polymerizes to form
paraformaldehyde, it is composed of repeating units of CH2O. The formula for
for this polymer is (CH2O) x. The more CH2O units that add into the structure, the
heavier the molecule becomes, until it precipitates out of solution in the form of
large paraffin-like flakes. This can be seen in bottles of embalming fluid that
have exceeded their shelf life or have been subjected to low temperatures.
Formaldehyde also tends to polymerize when subjected to low pH. As a result,
commercial arterial embalming fluids are buffered to approximately 6.5 to 9.0 as
a preventive measure. METHYL ALCHOL IS ROUTINELY INCLUDED
IN THE COMPOSITION OF ARTERIAL EMBELMING FLUIDS AS AN
ANTIPOLYMERIZING AGENT FOR FOMALDEHYDE.
Although paraformaldehyde (paraform) is undesirable in arterial fluids, it is
employed as a major preservative in solid autopsy compounds. When used in
this situation, the paraform is hydrolyzed by the moisture in the body tissues and
releases formaldehyde gas into the adjacent areas.
5. In very basic solutions, formaldehyde is unstable. Formaldehyde has a very
limited pH range. If the surrounding medium becomes too acidic, it polymerizes.
If that medium is too basic, it decomposes.
6. Formaldehyde reacts with ammonia to form urotropin.
6CH2O + 4NH3
(CH2)6N4+ 6H2O
The formation of urotropin demonstrates the affinity of formaldehyde for
nitrogen. This results in the neutralization of formaldehyde. Any source of
nitrogen can bring about this reaction. Nitrogen is an important part of proteins.
Therefore, as the proteins are broken down during decomposition, nitrogen is
released. The formaldehyde demand is increased. This means that more
formaldehyde above and beyond normal concentrations must be added in order to
overcome the elevated threshold generated by decomposition. This is similar to
the effect of hard water on soap in that a certain amount of the soap is used in
reacting with the hard-water minerals before the remaining portion is able to
function as a cleansing agent.
Decomposition is not the only situation that increases formaldehyde demand.
Uremic poisoning (urine in the blood) is an example of a pathological condition
that produces a similar effect. When renal dysfunction occurs, the urea is not
absorbed by the kidney tissues, resulting in dramatic increases of this toxic
substance in the circulating blood.
7. Formaldehyde cross-links proteins. This will be discussed later.
DIALDEHYDES
The dialdehydes are organic compounds containing two –CHO groups. They are
often incorporated in embalming fluids.
Dialdehydes like monoaldehydes are named as the reduction products of their
corresponding dicarboxylic acids.
GLYOXAL – The simplest of the dialdehydes, (CHO) 2, derives its name from
oxalic acid, its corresponding carboxylic acid which upon reduction produces
glyoxal. It also gets its name from ethylene glycol, an alcohol which produces
glyoxal on oxidation. Glyoxal is comparable in protein coagulability to
formaldehyde. The resultant yellow color makes its use in embalming fluid
undesirable. As previously stated, the stringency of organic compounds generally
decreases as the length of the carbon chain increases. As A result, the higher
dialdehydes have been investigated for possible application to embalming. Of these
higher dialdehydes, glutaraldehyde has been found to have the best application to
embalming.
O
H
H
H
H
H
C
C
C
C C
H
H
H
O
Glutaraldehyde
Two percent-activated glutaraldehyde has proved to be not only a good preservative,
but also an excellent germicide. In fact, this compound has been described as a “cold
chemical sterilant.” The term “activated” refers to the addition of a sodium
bicarbonate buffer, which stabilizes the pH of the resulting solution at approximately
7.2. Like formaldehyde, glutaraldehyde operates best at this pH. The one drawback
is that once the solution has been activated, it has an effective shelf life of only 14
days. However, this problem is circumvented by incorporating glutaraldehyde into
embalming fluid in an inactive state. When this fluid is ready to be used in an
embalming operation, the glutaraldehyde is activated by the addition of another
chemical called a coinjection, which contains the buffer.
Glutaraldehyde is much less astringent and dehydrating than formaldehyde. As a
result, tissue preserved in this manner is not as hard as formaldehyde-treated tissue
and retains much more of its original texture.
CYCLIC ALDEHYDES
The low-molecular-weight aldehydes have harsh, irritating odors. As the molecular
mass increases, the odors become more fragrant. Aromatic aldehydes are used as
perfuming agents in embalming fluids. Some examples are:
CHO
HC
C
H
H
C
O
OCH3
CHO
Benzaldehyde
(almonds)
Cinnamaldehyde
(cinnamon)
Anisaldehyde
(anise)
KETONES
Ketones are derivatives of hydrocarbons containing one or more carbonyl groups.
C
O
The carbonyl group is common to both aldehydes and ketones. We may distinguish
between aldehydes and ketones by the position of this group. If the carbonyl group
is placed at the end of a carbon chain, the compound is an aldehyde. If this group is
not on the end of the chain, the compound is a ketone. For example:
H
H
H
H
C
C C O
H
H
Aldehyde
H
H
O
H
C
C C H
H
H
Ketone
We can name ketones by changing the –e ending on the corresponding hydrocarbon
to –one. In this method, of naming, all of the carbons in the compound are counted
including the one in the carbonyl group. For example: CH3COCH3 is called
propanone because there are three carbons total..
Ketones are produced by the oxidation of secondary alcohols. Propanone is
produced by the oxidation of isopropyl alcohol. Propanone is also called dimethyl
ketone and acetone. This is the most important ketone as far as the embalmer is
concerned. It is an excellent solvent that will dissolve most organic substances yet is
completely miscible with water. It is sometimes incorporated into embalming fluids
as a solvent, but it could cause problems because it will dissolve plastic and is
thereby contraindicated for use with plastic hoses or plastic machine part. Acetone is
most valuable in embalming as an external solvent for removal of road tar or
bandage adhesive from the surface of the skin.