asphaltBitumen. See petroleum.aspirin(acetylsalicylic acid)an
acetylated form of *salicylic acid (1-
hydroxybenzoic acid), used exten-
sively as a medicinal drug; r.d. 1.4;
m.p. 138–140°C; b.p. 140°C (with de-
composition). It wasÜrst marketed in
1899 as a analgesic. The acid can be
obtained from willow bark and it has
long been known that the bark could
be used for pain relief and for the re-
duction of fever. The name salicylic
acid comes from the botanical name
of the willow (Salix alba). Aspirin acts
by suppressing the production of cer-
tain hormones (prostaglandins and
thromboxanes) by inhibiting the en-
zyme cyclooxygenase (COX). Conse-
quently, it is known as a ‘COX
inhibitor’. It is used for the treatment
of arthritis and to reduce body tem-
perature. It also acts as an anticoagu-
lant in the blood and small doses are
taken regularly to reduce the risk of
heart attack. A common side effect of
high doses is stomach bleeding and
stomach ulcers. Aspirin is made in-
dustrially from phenol, which with
concentrated sodium hydroxide and
carbon dioxide gives sodium phenox-
ide:
C 6 H 5 OH + NaOH →C 6 H 5 O–Na++
H 2 O.
The phenoxide ion undergoes elec-
trophilic substitution to give sodium
salicylate:
C 6 H 5 O–+ CO 2 + Na+→C 6 H 4
(OH)COO–Na+
With acid, this forms salicylic acid,
which can be acetylated in the ortho
position with ethanoic anhydride.associated liquidSee association.associationThe combination of
molecules of one substance with
those of another to form chemical
species that are held together by
forces weaker than normal chemicalbonds. For example, ethanol and
water form a mixture (an associated
liquid) in which hydrogen bonding
holds the different molecules to-
gether.astatineSymbol At. A radioactive
*halogen element; a.n. 85; r.a.m. 211;
m.p. 302°C; b.p. 337°C. It occurs nat-
urally by radioactive decay from ura-
nium and thorium isotopes. Astatine
forms at least 20 isotopes, the most
stable astatine–210 has a half-life of
8.3 hours. It can also be produced by
alpha bombardment of bismuth–200.
Astatine is stated to be more metallic
than iodine; at least 5 oxidation
states are known in aqueous solu-
tions. It will form interhalogen com-
pounds, such as AtI and AtCl. The
existence of At 2 has not yet been es-
tablished. The element was synthe-
sized by nuclear bombardment in
1940 by D. R. Corson, K. R. MacKen-
zie, and E. Segré at the University of
California.
A- Information from the WebElements site
Aston, Francis William
(1877–1945) British chemist and
physicist, who until 1910 worked at
Mason College (later Birmingham
University) and then with J. J. *Thom-
son at Cambridge University. In 1919
Aston designed the mass spectro-
graph (see mass spectroscopy), for
which he was awarded the Nobel
Prize for chemistry in 1922. With it
he discovered the *isotopes of neon,
and was thus able to explain noninte-
gral atomic weights.astrochemistry The study of mol-
ecules in interstellar space. Interstel-
lar molecules are usually detected
by their spectra in the radio, micro-
wave, or infrared regions of the elec-
tromagnetic spectrum. To date, over
140 different molecules have been
detected. Of special interest in astro-asphalt 46a