X
xanthan. A synthetic, water-soluble bipolymer respectively, are both dimethylxanthines; caffeine
made by fermentation of carbohydrates; it is a thick- in coffee is a trimethylxanthine.
ening and suspending agent that is heat stable, with Properties: Yellowish-white powder. Sublimes with
good tolerance for strongly acidic and basic solu- partial decomposition; soluble in potassium hydrox-
tions. Viscosity remains stable over wide tempera- ide; insoluble in water and acid.
ture range. Derivation: By the action of nitrous acid on guanine.
Use: In drilling fluids, ore flotation, and the food and Grade: Technical, CP, monohydrate, sodium salt,
pharmaceutical fields, especially in prepared mixed radioactive forms available.
and high-protein fast foods. An experimental use is Hazard: Toxic by ingestion.
to flood oil fields as an aid to enhanced recovery. Use: Organic synthesis, medicine.
xanthate. A salt (usually potassium or sodium) of xanthine oxidase. An enzyme found in animal
a xanthic acid. Available as yellow pelletized solids tissues that acts upon hypoxanthine, xanthine, alde-
having a pungent odor; soluble in water. Examples hydes, reduced coenzyme I, etc. producing, respec-
are potassium amyl xanthate, potassium ethyl xant- tively, xanthine, uric acid, acids, oxidized coenzyme
hate, sodium isobutyl xanthate, sodium isopropyl I, etc.
xanthate. Use: Biochemical research.
Use: Collector agents in the flotation of sulfide min-
erals, metallic elements such as copper, silver, gold,
xanthogenic acid. See xanthic acid.
and some oxidized minerals of lead and copper.
See cellulose xanthate; viscose process.
xanthone. (benzophenone oxide; dibenzopy-
rone; xanthene ketone).
xanthene. (dibenzopyran, tricyclic).
CAS: 90-47-1. CO(C
6
H
4
)
2
O. Tricyclic; occurs in
CH
2
(C
6
H
4
)
2
O. The central structure of the fluoros-
some plant pigments.
cein, eosin, and rhodamine dyes.
Properties: White needles or crystalline powder. Mp
Properties: Yellowish, crystalline leaflets. Mp
173–4C, bp 350C, sublimes. Insoluble in water;
100.5C, bp 315C. Soluble in ether; slightly soluble
soluble in alcohol, chloroform, and benzene, espe-
in alcohol; very slightly soluble in water.
cially when hot.
Derivation: By the condensation of phenol and o-
Use: Larvicide; intermediate for dyes, perfumes, and
cresol by means of aluminum chloride.
pharmaceuticals.
Use: Organic synthesis, fungicide.
xanthophyll.
C
40
H
56
O
2
.
xanthene dye. A group of dyes whose molecu-
Properties: Yellow pigment. An oxygenated carot-
lar structure is related to that of xanthene. The aro-
enoid occurring in green vegetation and in some
matic (C
6
H
4
) groups constitute the chromophore. CI
animal products, notably egg yolk. Mp 190–3C.
ranges from 45000 to 45999. The dyes are closely
Insoluble in water; slightly soluble in alcohol and
related structurally to diaryl methane dyes. Eosin
ether.
(CI 45380) is an example.
See lutein; carotenoid.
xanthenol. See xanthydrol.
xanthopterin. (2-amino-4,6-dihydroxypteri-
dine). C
6
H
5
N
5
O
2
•H
2
O. Pigment found in the wings
xanthic acid. (xanthogenic acid). A substitut- of butterflies; can be converted by yeast into folic
ed dithiocarbonic acid of the type ROC(S)SH, in acid.
which R is ordinarily an alkyl radical. Xanthic acid Properties: Orange-yellow crystals. Sinters at 360C,
salts are called xanthates. Unless otherwise desig- decomposes above 410C. Practically insoluble in
nated, xanthic acid is understood to be the ethyl water; freely soluble in dilute ammonium or sodium
derivative (C
2
H
5
OC(S)SH), also called ethylxanthic hydroxide giving yellow solutions and in 2N hydro-
acid. chloric acid giving colorless solutions.
Properties: Liquid. Mp −53C, decomposing at room Use: Biochemical research.
temperature.
xanthydrol. (xanthenol).
xanthine. (dioxopurine). CAS: 90-46-0. HCOH(C
6
H
4
)
2
O. A derivative of
CAS: 69-89-6. C
5
H
4
N
4
O
2
. A purine base occurring in
xanthene.
the blood and urine and in some plants. Theophyl- Properties: White powder. Mp 123C. Insoluble in
line and theobromine, the alkaloids of tea and cocoa, water; soluble in alcohol.
1334
1335 X-RADIATION
Derivation: Reduction of xanthone with alcohol and Complex compounds containing nitrogen bonded to
sodium. xenon have also been prepared.
Grade: CP (analytical). Hazard: Toxic by inhalation; oxidizing agents,
Use: Determination of urea and DDT. strong irritant.
xatral. xenyl. The biphenyl group C
6
H
5
C
6
H
4
−.
CAS: 81403-68-1. mf: C
19
H
27
N
5
O
4
•ClH.
Hazard: A poison.
p-xenylamine. See p-aminodiphenyl.
X chromosome. One of the two sex chromo- xerography. A “dry” method of photography or
somes, X and Y. photocopying. A metal plate is covered with a layer
See Y chromosome; sex chromosome. of photoconductive powder, such as selenium; the
surface of this plate is given an electric charge by
passing it under a series of charged wires. An image
Xe. Symbol for xenon.
of the material to be photographed is projected onto
the charged plate through a camera lens. The electric
xenograft. Tissue or organs from an individual of
charges disappear in the areas exposed to light, but
one species transplanted into or grafted onto an
elsewhere the surface retains its charge. A powder
organism of another species, genus, or family. A
consisting of a coarse carrier and a fine developing
common example is the use of pig heart valves in
resin is then spread over the plate. Adhesion be-
humans.
tween powder and plate occurs only at the charged
areas. Elsewhere developing resin and carrier are
3-(2-xenolyl)-1,2-epoxypropane.
not retained on the plate, which thus has become a
Use: Food additive; plasticizer.
negative of the original image. A positive is ob-
tained by placing a piece of paper against the plate
xenon. Xe. Element of atomic number 54, noble
and applying an electric charge as in the first stage of
gas group of the periodic table, aw 131.30, valences
the process. This causes adhesion of developing
=
2, 4, 6, 8; nine stable isotopes.
resin and its carrier to the paper. This positive print is
Properties: Colorless, odorless gas or liquid. Gas (at
fixed by heating in a press for a few seconds to melt
STP) has d 5.8971 g/L (air
=
1.29 g/L), dielectric
the developing resin and fuse it to the paper. Colored
constant 1.0012 (25C) (1 atm); liquid has bp
prints are possible by use of suitable developing
−108.12C (1 mm Hg), d (at bp) of 1.987 g/cc; lique-
resins. Various materials other than paper can thus
faction temp −106.9C. Chemically unreactive but
be printed.
not completely inert. Noncombustible.
Derivation: Fractional distillation of liquid air.
xibornol. (6-isobornyl-3,4-xylenol). C
18
H
26
O.
Use: Luminescent tubes, flash lamps in photography,
Properties: Crystalline solid or viscous, yellowish
fluorimetry, lasers, tracer studies, anesthesia.
liquid. D 1.02, refr index 1.538.
See noble gas; xenon compounds.
Use: Antibacterial agent, rubber antioxidant.
xenon compounds. Xenon tetrafluoride, XeF
4
,
X-linked. Shortened form for cross-linked, e.g.,
is easily prepared by mixing fluorine and xenon in
X-linked polyethylene.
gaseous form, heating in a nickel vessel to 400C, and
cooling. The product forms large, colorless crystals.
XLPE. Trade abbreviation for cross-linked poly-
The difluoride and hexafluoride, XeF
2
and XeF
6
,
ethylene.
also colorless crystals, can be obtained somewhat
similarly. The hexafluoride melts to a yellow liquid
XPS. Abbreviation for X-ray photoelectron spec-
at 50C and boils at 75C. Many xenon fluorine com-
troscopy.
plexes with other compounds are also known. Xe-
non oxytetrafluoride, XeOF
4
, a volatile liquid at
room temperature, is obtained from the reaction of
x-radiation. (Roentgen rays; x rays). Electro-
xenon hexafluoride and silica. Gram amounts have magnetic radiation of extremely short wavelength
been isolated and studied. (0.06–120 A
˚
), emitted as the result of electron tran-
All these fluorides must be protected from moisture sitions in the inner orbits of heavy atoms bombarded
to avoid formation of xenon trioxide, XeO
3
, a color- by cathode rays in a vacuum tube. Those of the
less, nonvolatile solid that is dangerously explosive shortest wavelength have the highest intensity and
when dry. Its solution, the so-called xenic acid, is a are called “hard” X rays. X-radiation was discov-
stable weak acid but a strong oxidizing agent, which ered by Roentgen in 1898. Its properties are (1)
will even liberate chlorine from hydrochloric acid. penetration of solids of moderate density, such as
In an alkaline solution, xenon trioxide reacts to give human tissue but retardation by bone, barium sul-
free xenon and perxenate, such as Na
4
XeO
6
•8H
2
O. fate, lead, and other dense materials. (2) Action on
Perxenates are probably the most powerful oxidiz- photographic plates and fluorescent screens. (3) Ion-
ing agents known, just as the xenon fluorides are ization of the gases through which they pass. (4)
extremely effective fluorinating agents. Ability to damage or destroy diseased tissue; there is
1336“XYDAR”
also a cumulative deleterious effect on healthy thesis, especially isophthalic acid; insecticides; avi-
tissue. ation fuel.
Hazard: Overexposure can permanently damage
cells and tissue structures; effect is cumulative.
m-xylene-␣,␣
′
-diamine. (MXDA; m-pheny-
Use: Spectrometry; structure determination of mole-
lenebis(methylamine)).
cules, cancer therapy, diagnostic medicine, nonde-
CAS: 1477-55-0. mf: C
8
H
12
N
2
.
structive testing of metals, identification of original
Properties: A liquid. Mw 136.22, bp 245−248C.
paintings, preservation of foods.
Hazard: Moderately toxic by skin contact and inges-
See radiation, ionizing; diffraction; roentgen.
tion. Mildly toxic by inhalation. A severe skin and
eye irritant. TLV: TWA ceiling of 0.1 mg/m
3
. Toxic
“Xydar” Solvay Advanced. TM for liquid
by skin absorption.
crystal polymer glass/mineral combination product.
Use: Manufacture of polyamide fibers and resins, as a
Use: Microwave cabinets; cookware; automotive and
curing agent.
electronic components.
o-xylene. (1,2-dimethylbenzene).
xylene. (dimethylbenzene).
CAS: 95-47-6. 1,2-C
6
H
4
(CH
3
)
2
.
CAS: 1330-20-7. C
6
H
4
(CH
3
)
2
. A commercial mix-
Properties: Clear, colorless liquid. D 0.880 (20/4C),
ture of the three isomers, o-, m-, and p-xylene. The
fp −25C, bp 144C, refr index 1.505 (20C), flash p
last two predominate.
115F (46.1C) (TOC), autoign temp 867F (463.8C).
Properties: Clear liquid. D about 0.86. See under
Soluble in alcohol and ether; insoluble in water.
Grade for boiling range, flash p 81–115F
Combustible.
(27.2–46.1C) (TOC). Soluble in alcohol and ether;
Grade: 99%, free of hydrogen sulfide and sulfur
insoluble in water.
dioxide, technical 95%, research 99.9%.
Derivation: (1) Fractional distillation from petrole-
Hazard: Moderate fire risk. TLV: 100 ppm; STEL
um (90%), coal tar, or coal gas, (2) by catalytic
150 ppm; not classifiable as a human carcinogen.
reforming from petroleum, followed by separation
Use: Manufacture of phthalic anhydride, vitamin and
of p-xylene by continuous crystallization, (3) from
pharmaceutical syntheses, dyes, insecticides, motor
toluene by transalkylation.
fuels.
Grade: Nitration (bp range 137.2–140.5C), 4 de-
grees (bp range 138–134C), 5 degrees (bp range
137–142C, high in m-isomer), 10 degrees (bp range
135–145C), industrial (bp 90% 40C, complete
160C). Also other grades depending on use. In some
cases one or another of the industrial isomers is
partially removed for use in chemical production.
Hazard: Flammable, moderate fire risk. Toxic by
ingestion and inhalation. TLV: 100 ppm; STEL 150
p-xylene. (1,4-dimethylbenzene).
ppm; not classifiable as a human carcinogen.
CAS: 106-42-3. 1,4-C
6
H
4
(CH
3
)
2
.
Use: Aviation gasoline; protective coatings; solvent
for alkyd resins, lacquers, enamels, rubber cements;
synthesis of organic chemicals.
m-xylene. (1,3-dimethylbenzene).
CAS: 108-38-3. 1,3-C
6
H
4
(CH
3
)
2
.
Properties: Colorless liquid. D 0.8611 (20C), mp
13.2C, bp 138.5C, refr index 1.5004 (21C), flash p
81F (27.2C) (TOC). Crystallizes at low temperature.
Soluble in alcohol and ether; insoluble in water.
Derivation: Selective crystallization or solvent ex-
Properties: Clear, colorless liquid. D 0.8684 (15C),
traction of m-, p-mixture; separation from mixed-
fp −47.4C, bp 138.8C, refr index 1.4973 (20C), flash
xylene feedstocks by adsorption.
p 85F (29.4C), autoign temp 982F (527.7C). Soluble
Hazard: Flammable, dangerous fire risk. TLV: 100
in alcohol and ether; insoluble in water.
ppm; STEL 150 ppm; not classifiable as a human
Derivation: Selective crystallization or solvent ex-
carcinogen.
traction of m, p-mixture.
Use: Synthesis of terephthalic acid for polyester res-
Grade: 95% (technical), 99%, 99.9% (research).
ins and fibers (“Dacron,” “Mylar,” “Terylene”), vi-
Hazard: Flammable, moderate fire risk. TLV: 100
tamin and pharmaceutical syntheses, insecticides.
ppm; STEL 150 ppm; not classifiable as a human
carcinogen.
Use: Solvent; intermediate for dyes and organic syn-
p-xylene-␣,␣
′
-diol. C
6
H
4
(CH
2
OH)
2
.
1337 ((2,6-XYLYL)SULFINYL)
Properties: White, crystalline solid. Mp 118C, bp
xylocaine. Preparation of lignocaine hydrochlo-
138–144C (0.8–1.0 mm Hg). Slightly soluble in ride.
water (25C). Use: Local anesthetic.
Grade: 98%.
Use: Polyester resins.
xylol. Commercial-grade xylene, a mixture of iso-
mers and other benzene derivatives.
xylenol. (dimethylphenol; hydroxydimethylben-
xylopic acid.
zene; dimethylhydroxybenzene).
Properties: Xylopia aethiopica. Family Annonacea.
CAS: 1300-71-6. (CH
3
)
2
C
6
H
3
OH. There are five iso-
CAS: 6619-97-2. mf: C
22
H
32
O
4
.
mers (2,4-; 2,5-; 2,6-; 3,4-; 3,5-). This entry de-
Hazard: A poison by ingestion.
scribes the commercially offered mixture.
D(+)-xylose. (wood sugar).
CAS: 58-86-6. C
5
H
10
O
5
. (not to be confused with
phenylosazone of the same name).
Properties: White, crystalline, dextrorotatory pow-
der; sweet taste. D 1.525 (20C), mp 144C (also given
as 153C). Soluble in water and alcohol. Combus-
tible.
Derivation: Hydrolysis with hot dilute acids of
Properties: White, crystalline solid. D 1.02–1.03
wood, straw, corncobs, etc.; wood pulp wastes.
(15C), mp 20–76C, bp 203–225C. Only slightly
Grade: Reagent, technical.
soluble in water; soluble in most organic solvents
Use: Dyeing, tanning, diabetic food, source of eth-
and caustic soda solution. Combustible.
anol.
Derivation: Cresylic acid or tar acid fraction of coal
tar.
xylyl bromide. (␣-bromoxylene).
Hazard: Toxic by ingestion and skin absorption.
CAS: 35884-77-6. CH
3
C
6
H
4
CH
2
Br. Mixed o-, m-,
Use: Disinfectants, solvents, pharmaceuticals, insec-
and p-isomers.
ticides and fungicides, plasticizers, rubber chemi-
Properties: Colorless liquid; pleasant aromatic odor.
cals, additives to lubricants and gasolines, manufac-
Decomposed slowly by water, d 1.4, bp 210–220C.
ture of polyphenylene oxide (2,6-isomer only),
Combustible.
wetting agents, dyestuffs.
Derivation: Bromination of xylene.
Grade: Technical.
Hazard: Toxic by inhalation and ingestion; strong
xylidine. (aminodimethylbenzene; aminoxy-
irritant to eyes, skin, and tissue.
lene).
Use: Organic synthesis, tear gas.
CAS: 1300-73-8. (CH
3
)
2
C
6
H
3
NH
2
. A varying mix-
ture of isomers (2,3-; 2,4-; 2,5-; 2,6-).
m-xylyl chloride. CH
3
C
6
H
4
CH
2
Cl.
Properties: Colorless liquid. Bp 196, d 1.064. Com-
bustible.
Hazard: Toxic by ingestion and inhalation, strong
irritant to eyes and skin.
Use: Intermediate.
p-xylylene. CH
2
:C
6
H
4
:CH
2
. A monomer.
Properties: Liquid. D 0.97–0.99, bp 213–226C,
See parylene.
flash p 206F (96.6C) (CC). Slightly soluble in water;
soluble in alcohol and ether. Combustible.
n-2,3-xylylmaleimide.
Derivation: Nitration of xylene and subsequent re-
CAS: 31581-09-6. mf: C
12
H
11
NO
2
.
duction.
Hazard: Low toxicity by ingestion and inhalation. A
Hazard: Toxic by ingestion, inhalation, and skin
severe eye irritant.
absorption. TLV: 0.5 ppm; animal carcinogen.
Use: Dye intermediate, organic syntheses, pharma-
((2,6-xylyl)sulfinyl)methylcarbamic acid-
ceuticals.
2,3-dihydro-2,2-dimethyl-7-benzofuranyl
ester.
3,4-xylidino-2-oxazoline. CAS: 77248-44-3. mf: C
20
H
23
NO
5
S.
CAS: 23420-61-3. mf: C
11
H
14
N
2
O. Hazard: A poison by ingestion.
Hazard: A poison. Use: Agricultural chemical.
