PARAFORMALDEHYDES
Synthesis and Applications
By
Hoang Le
Chem12B-Spring 2006
ABSTRACT
Paraformaldehydes, the polymer of
formaldehydes, are the most commonly used
fixatives. They serve to stabilize the fine structural
details of cells and tissues prior to examination by
light or microscopy. Beside fixatives function,
paraformaldehydes can be used as decontaminant.
Even though paraformaldehydes have many useful
applications, they usually give unpleasant odors
and are toxic substances. This presentation will
briefly describe what are paraformaldehydes, their
applications and their effects on human health.
OUTLINE
1.
2.
3.
4.
5.
Why did I choose paraformaldehydes?
Paraformaldehydes, what they are and
what they do?
Toxicity of paraformaldehydes
Comparison with others food
preservation
Conclusions
Why chose
Paraformaldehydes?
1. Curiosity in how animal’s tissues are
preserved in biology lab.
2. Anthrax crisis in 2002 and the need of
decontamination.
3. Its toxicity when it was used to preserve
food.
Paraformaldehydes
What they are?
1.
2.
3.
A polymer of formaldehydes
A white crystalline powder with the
odor of formaldehyde.
Have chemical formular of (-HCHO-)n
with n = 2 to 100
Paraformaldehydes
the systhesis
Paraformaldehydes can be synthesize by dissolve
rapidly formaldehyde gas in water, with which they
combine chemically to form methylene hydrate.
HO-CH2-OH
Methylene hydrate molecules react with one
another, combining to form polymer.
Synthesis mechanism
H2O + H C=O
H
HO-CH2-OH
Methylene hydrate
formaldehyde
n HO-CH2-OH
H-CH2-O-OH
n
Formaldehyde polymer
Paraformaldehyes
Applications


Paraformaldehydes are widely used
fixative. They have been used over
century as a tissue preservative.
Paraformaldehyes have been used as a
decontaminant for more than 30 years.
Fixatives
To be useful as a fixative, paraformaldehydes
first have to be broken down to monomeric
formaldehyde. Formaldehyde then reacts with
active hydrogens atom of protein to form
cross-link -CH2- called methylene bridge. This
is Nucleophillic Addition reaction of amines to
aldehyde.
Fixative mechanism.
Step 1: depolymerization of paraformaldehydes
H2
C
O
H2
C
O
H2
C
O
H2
C
Paraformaldehyde
(4 units within large polymer)
O
60oC
(OH-)
4
H
C=O
H
Formaldehyde
(4 molecules)
Step 2: cross-link formation
PROTEIN -H + HCHO
PROTEIN -HCHOH
PROTEIN
PROTEIN -HCHOH
+ H- PROTEIN
C PROTEIN
H2
Methylene bridge
+ H2O
Decontaminant



When heated releases formaldehyde gas,
which can be used as decontaminant.
Use to control harmful microorganisms such
as bacteria, viruses, or fungi on inanimate
objects and surface.
Formaldehyde inactivate protein by forming
covalent cross-links with several organic
functional groups on protein.
Federal Anthrax decontamination


During the course of October 2001,
several government and commercial
building were contaminated with spores
of Bacillus anthracis, commonly known
as anthrax.
EPA had identified paraformaldehydes
as potentially substance for anthrax
decontamination.
Toxicity of paraformaldehydes



When heated, paraformaldehydes produce
fomaldehyde gas which identified as a mutagen
and a carcinogen.
Paraformaldehyde will inactivate and destroy
proteins on cell membrane as well as in the tissue.
As the result, the proteins will loose its functions.
Cause damage to sight, cause skin or eye burns or
irritation, cause severe burning of mouth and
stomach, and cause heritable genetic damage.
Comparison with other food
preservative


The regular food preservatives are not toxic
because they only target microorganism that
cause food spoilage but they won’t affect
human proteins. Food preservatives prevent
protein synthesis in microorganism by
targeting the function of 70s ribosome.
Common food preservatives are Sulfur oxide,
Sorbic acid, sodium benzoate, calcium
propionate, and sodium nitrate.
Conclusion
Paraformaldehydes were used as a tissue
preservative for over a century. They were also
used to decontaminate the surfaces which were
contaminated by harmful microorganism.
However, paraformaldehydes are toxic and
harmful to human health and environment.
Therefore, we need to have tight control and
regulation for the manufacture and usage of
paraformaldehydes.
References
Helander, K.G.(1994). Kinetic studies of formaldehyde binding in tissue. Biotechnic &
Histochemistry 69: 177-179.
Hopwood, D. (1969). Fixatives and fixations: a review. Histochemical Journal 1: 323-360.
http://publish.uwo.ca/~jkiernan/formglut.htm
http://www.epa.gov/pesticides/factsheets/chemicals/paraformaldehyde_factsheet.html
http://aic.stanford.edu/jaic/articles/jaic29-02-004_4.html
http://ptcl.chem.ox.ac.uk/MSDS/PA/paraformaldehyde.html
http://www.inchem.org/documents/ehc/ehc/ehc89.htm#SectionNumber:3.2