BORON 119
4. CHEMICAL AND PHYSICAL INFORMATION
4.1 CHEMICAL IDENTITY
Boron appears in Group 13 (IIIA) of the periodic table and is the only nonmetal of this group (Jansen
2003). Table 4-1 lists common synonyms, trade names, and other pertinent information to identify boron
and selected compounds.
4.2 PHYSICAL AND CHEMICAL PROPERTIES
Boron is a nonmetal and is typically found in nature bound to oxygen. It is never found as the free
element (Cotton et al. 1999). Boron has two stable isotopes,
10
B and
11
B, which are naturally present at
19.10–20.31 and 79.69–80.90%, respectively (Jansen 2003). There are ten other known non-radioactive
isotopes of boron (Lide 2008). Elemental boron exists in several allotropic forms (Jansen 2003). In
addition to being an amphorous powder, boron has four crystalline forms: α-rhombohedral,
β-rhombohedral, α-tetragonal, and β-tetragonal (Jansen 2003).
The chemical properties of boron are more similar to carbon and silicon than elements of its own group,
although boron is more electron deficient. Boron has a high affinity for oxygen-forming borates, and
reacts with water at temperatures above 100 °C to form boric acid and other boron compounds. The
electron deficiency of boron does not allow conventional two-electron bonds, but rather multicenter bonds
that are exclusively covalent (Jansen 2003; Schubert and Brotherton 2006). Boron hydrides consequently
have structures quite different from hydrocarbons (Jansen 2003). The multi-center nature of boron allows
the formation of a diverse array of covalent networks, rings, cages, and clusters. Boron forms strong
covalent bonds with electronegative elements such as fluorine and oxygen (Schubert and Brotherton
2006).
Table 4-2 lists important physical and chemical properties of boron and selected compounds.
BORON 120
4. CHEMICAL AND PHYSICAL INFORMATION
Table 4-1. Chemical Identity of Boron and Selected Boron Compounds
a
Characteristic
Boron
Boron oxide
Boric acid
Synonym(s) Boron, metallic
Boric anhydride; boric
acid, anhydride; boron
sesquioxide; boron
trioxide; diboron trioxide;
fused boric acid
Orthoboric acid; boron
hydroxide; boron
trihydroxide
Registered trade
name(s)
No data No data
Optibor
b
Chemical formula
Chemical structure
B
Amphorous powder, as
well as four crystalline
forms: α-rhombohedral,
β-rhombohedral,
α-tetragonal, and
β-tetragonal
c
B
2
O
3
Randomly oriented B
3
O
3
rings with bridging
oxygen atoms
d
B(OH)
3
Planar BO
3
3-
units linked by
asymmetrical hydrogen
bonds
d
Identification numbers:
CAS registry
7440-42-8
1303-86-2
10043-35-3
NIOSH RTECS
e
ED7350000
ED7900000
ED4550000
EPA hazardous waste
No data
No data
No data
EPA/OPP pesticide
Code
128945 011002 011001
OHM/TADS
No data
No data
No data
DOT/UN/NA/IMDG
shipping
No data
No data
No data
HSDB
4482
1609
1432
EINECS
231-151-2
215-125-8
233-139-2
NCI
No data
No data
C56417
BORON 121
4. CHEMICAL AND PHYSICAL INFORMATION
Table 4-1. Chemical Identity of Boron and Selected Boron Compounds
a
Characteristic
Borax
Sodium tetraborate
Boron tribromide
Synonym(s)
Sodium borate; sodium
Sodium borate; sodium
Boron bromide; tribromo-
tetraborate; borax
borate anhydrous;
borane; tribromoboron
decahydrate; disodium
disodium tetraborate;
tetraborate decahydrate
sodium biborate; sodium
pyroborate; boric acid,
disodium salt
Registered trade
name(s)
Jaikin, Pyrobor, Three
Elephant, V-Bor
b
Dehybor 65
b
No data
Chemical formula
B
4
Na
2
O
7
•10H
2
O
Na
2
B
4
O
7
BBr
3
Chemical structure
Anhydrous borates have
polymeric assemblies of
2-
planar BO
3
and/or
tetrahedral BO
4
units
OH
HO
linked by shared oxygen
atoms
d
Br
Br
Tetraborate anion in
solution
d
Identification numbers:
CAS registry
1303-96-4
1330-43-4
10294-33-4
NIOSH RTECS
e
VZ2275000
ED4588000
ED7400000
EPA hazardous waste
No data
No data
No data
EPA/OPP Pesticide
029601
011112
No data
Code
OHM/TADS No data No data No data
DOT/UN/NA/IMDG
No data No data UN 2692; IMDG 8.1
shipping
HSDB
328
5025
327
EINECS
233-139-2
215-540-4
233-657-9
NCI
No data
No data
No data
Br
B
O
B
O
B
O
B
O
B
O
OH
OH
BORON 122
4. CHEMICAL AND PHYSICAL INFORMATION
Table 4-1. Chemical Identity of Boron and Selected Boron Compounds
a
Characteristic
Boron trifluoride
Boron trichloride
Synonym(s)
Anca 1040; boron fluoride; Trichloroborane;
trifluoroborane trichloroboron
Registered trade
No data
No data
name(s)
Chemical formula
BF
3
BCl
3
Chemical structure
F
F
B
F
Identification numbers:
CAS registry
7637-07-2
10294-34-5
NIOSH RTECS
e
ED2275000
ED1925000
EPA hazardous waste
No data
No data
EPA/OPP Pesticide
No data
No data
Code
OHM/TADS No data No data
DOT/UN/NA/IMDG UN 1008; IMDG 6.1
UN 1741; IMDG 2.2
shipping (boron trifluoride); UN
2851; IMDG 8.2 (boron
trifluoride dihydrate)
HSDB
325
326
EINECS
231-569-5
233-658-4
NCI
No data
No data
a
All information obtained from HSDB 2009 and ChemIDplus 2009, except where noted.
b
NIOSH 2005
c
Jansen 2003
d
Cotton et al. 1999
e
RTECS 2007
CAS = Chemical Abstracts Service; DOT/UN/NA/IMDG = Department of Transportation/United Nations/North
America/Intergovernmental Maritime Dangerous Goods Code; EINECS = European Inventory of Existing Chemical
Substances; EPA = Environmental Protection Agency; HSDB = Hazardous Substances Data Bank; NCI = National
Cancer Institute; NIOSH = National Institute for Occupational Safety and Health; OHM/TADS = Oil and Hazardous
Materials/Technical Assistance Data System; RTECS = Registry of Toxic Effects of Chemical Substances
BORON 123
4. CHEMICAL AND PHYSICAL INFORMATION
Table 4-2. Physical and Chemical Properties of Boron and Selected Boron
Compounds
a
Property Boron Boron oxide Boric acid
Molecular weight
10.811
69.620
61.833
Physical Black or dark brown powder Colorless, glassy or
Colorless, transparent
description (amorphous form); clear red hexagonal crystals,
crystals; white granules or
crystals (α-rhombohedral
hygroscopic
powder
form); black, opaque
crystals with metallic luster
(α-tetragonal form); black
(β-rhombohedral form)
Melting point
2,075 °C
450 °C (crystal)
170.9 °C
Boiling point
4,000 °C
1,500 °C (crystal)
No data
Density
2.350 g/cm
3
(amorphous);
2.46 g/cm
3
1.8 g/cm
3
(amorphous);
2.46 g/cm
3
(crystal)
1.435 g/cm
3
at 15 °C
(α-rhombohedral);
2.31 g/cm
3
(α-tetragonal);
2.35 g/cm
3
(β-rhombohedral)
Odor
No data
Odorless
Odorless
Solubility:
Water
Insoluble
4.0% at 20 °C
50 g/L at 25 °C
Organic
Insoluble alcohol, ether
Soluble in alcohol,
17.5% in glycerol; 18.5% in
solvent(s) glycerol ethylene glycol; 173.9 g/L in
methanol; 94.4 g/L in ethanol;
0.6% in acetone; 1.5% in ethyl
acetate (all at 25 °C)
Other
Soluble in concentrated
No data
No data
nitric and sulfuric acids
pK
a
No data
No data
9.42
Log K
ow
No data
No data
0.175
Vapor pressure
0.0119 mm Hg at 2,140 °C
Negligible at 20 °C
Negligible at 20 °C
Autoignition
580 °C No data No data
temperature
Flashpoint
No data
No data
No data
Flammability
Dust ignites spontaneously
Noncombustible
Not flammable
limits in air
in air
Conversion
No data No data No data
factors
Explosive limits
No data
No data
No data
BORON 124
4. CHEMICAL AND PHYSICAL INFORMATION
Table 4-2. Physical and Chemical Properties of Boron and Selected Boron
Compounds
a
Property
Borax
Sodium tetraborate
Boron tribromide
Molecular weight 381.373 201.220 250.52
Physical
White, monoclinic crystals
Colorless glassy solid;
Colorless, fuming liquid
Description
hygroscopic
Melting point
75 °C (decomposes)
743 °C
-46.0 °C
Boiling point
No data
1,575 °C (decomposes)
90 °C
Density
1.73 g/cm
3
2.367 g/cm
3
2.698 g/cm
3
at 0 °C
Odor
Odorless
Odorless
Sharp, irritating odor, pungent
Solubility:
Water
59.3 g/L at 25 °C
3.1% at 25 °C
Decomposes in water
Organic 1 g/1 mL in glycerol; 16.7% in methanol; 30%
Decomposes in alcohol;
solvents insoluble in alcohol in ethylene glycol;
soluble in carbon
40.6 g/L in formamide (all
tetrachloride, sulfur dioxide
at 25 °C)
(liquid), carbon disulfide
Other
Insoluble in acid
No data
No data
pK
a
No data
No data
No data
Log K
ow
No data
No data
No data
Vapor pressure Negligible Negligible at 20 °C 100 mm Hg at 33.5 °C
Autoignition
No data No data No data
temperature
Flashpoint
No data
No data
No data
Flammability
Not flammable
Noncombustible
Nonflammable
limits in air
Conversion
No data No data
1 ppm=10.25 mg/m
3b
factors
Explosive limits
No data
No data
No data
BORON 125
4. CHEMICAL AND PHYSICAL INFORMATION
Table 4-2. Physical and Chemical Properties of Boron and Selected Boron
Compounds
a
Property
Boron trifluoride
Boron trichloride
Molecular weight
67.81
117.17
Physical
Colorless gas Colorless fuming liquid at low temperature
Description
Melting point
-126.8 °C
-107 °C
Boiling point
-101 °C
12.5 °C
Density
3.07666 g/L at 1 atm, 0 °C
1.3728 g/cm
3
at 0 °C
Odor
Pungent, suffocating odor, irritating
c
Pungent, suffocating odor, irritating, sharp
Solubility:
Water
332 g/100 g water at 0 °C with some
Decomposes in water, hydrolyzed easily
hydrolysis forming fluoboric and boric
acids
Organic
Soluble in benzene, dichlorobenzene,
Decomposes in alcohol
solvents chloroform, carbon tetrachloride, carbon
sulfide; soluble in most saturated and
halogenated hydrocarbons and in
aromatic compounds
Other
1.94 g/100 g in anhydrous sulfuric acid,
No data
soluble in concentrated nitric acid
pK
a
No data
No data
Log K
ow
No data
No data
Vapor pressure
3.656x10
4
mm Hg at -13.2 °C
1 mm Hg at 25 °C (extrapolated)
Autoignition
No data No data
temperature
Flashpoint
No data
No data
Flammability
Nonflammable
Nonflammable
limits in air
Conversion
1 ppm=2.77 mg/m
3b
No data
factors
Explosive limits
No data
No data
a
All information from HSDB 2009, except where noted.
b
NIOSH 2009
c
Odor threshold 4.50 mg/m
3
(Ruth 1986)