1,4-Bis[(1-methyl-1-phenylethyl)peroxymethyl]benzene

The title compound, C₂₆H₃₀O₄, is one of the first alkyl bis-peroxides to be structurally characterized. The mol­ecule lies on a centre of inversion and therefore the terminal phenyl rings are parallel. Although there are three aromatic rings in the mol­ecule, the C-O-O-C torsion angle of 163.10 (10)° is close to the value found in Me₃COOCMe₃.

S1. Comment

Growing interest in fine chemicals has resulted in, inter alia, a rapid development in studies of organic peroxides. These compounds are able to initiate polymerization processes, as well as to crosslink unsaturated compounds (Sanchez & Myers, 1996). Recently, work has focused on molecules with several initiating peroxide and/or azo groups (Hazer, 1997), which may act as precursors for block or graft copolymers. Our previous study has shown that bis-peroxides can be obtained with good yields under phase-transfer catalysis conditions (Zawadiak et al., 2001). To our surprise, a search of the Cambridge Structural Database (April 2002, Version 1.4; Allen & Kennard, 1993) indicated only one crystal structure of an alkyl bis-peroxide to date (bisperoxyacetal; Jefford et al., 1984). Here, we report the results of X-ray crystallographic studies of 1,4-bis[(1-methyl-1-phenylethyl)peroxymethyl]benzene, (I). \sch

The molecule of (I) (Fig. 1) is symmetrical, with the central phenyl ring lying on a centre of inversion at (3/4,3/4,1/4). The C4—O1—O2—C5 dihedral angle of 163.10 (10)° is very close to that found in the simple analogous compound Me₃C—O—O-CMe₃ [166 (2)°; Käss et al., 1977]. The C—O—O—C dihedral angles in peroxides span a broad range, from 90.2 (6)° for H₂O₂ (Busing & Levy, 1965) to 180° for peroxides with very bulky groups near to the COOC fragment [e.g. Ph₃CO-OCPh₃ (Glidewell et al., 1979) or isopropylphenyl-9-fluorenyl peroxide (Robinson et al., 1999)]. The O—O bond distance in the peroxide group of (I) is 1.476 (2) Å (1.480 Å in Me₃CO-OCMe₃). Thus, it seems that the presence of aryl substituents on both sides of the C—O—O—C group and the absence of methyl substituents on one of its sides have no influence on the geometry of this group in comparison with Me₃C—O—O-CMe₃, or the effects cancel each another out.

Because the environment of each C atom in the C—O—O—C fragment is different, we also observe different C—O bond lengths and angles on each side of the bond. For the quaternary C5 atom, C5—O2 is 1.438 (2) Å and C5—O2—O1 is 107.3 (1)°, while for the secondary C4 atom, C4—O1 is 1.430 (2) Å and C4—O1—O2 is 104.3 (2)°. The small differences in the geometry of these C atoms, while statistically relevant, are easily explained by the presence of two more relatively bulky methyl groups attached to atom C5. For the same reason, we observe a slight lengthening of the C_alkyl—C_aryl bond in the case of the quaternary atom C5 [C5—C8 1.522 (2) Å] in comparison with the secondary atom C4 [C4—C2 1.495 (3) Å].

The terminal aromatic rings are parallel to each other (by symmetry), and the mean planes of the terminal and central aromatic rings form a dihedral angle of 42.9 (1)°. Weak intramolecular C—H···π interactions for C9—H9···Cg1 [C—H 0.95 (2), H···Cg1 2.84 (2) and C···Cg1 3.480 (2) Å, and C—H···Cg1 126 (1)°; Cg1 is the centroid of the central ring, C1/C2/C3/C1A/C2A/C3A] may, to some extent, control the twisted conformation of the whole molecule. Another weak C—H···π interaction is an intermolecular one, namely C7—H73···Cg2(3/2 - x, y, -z) [C—H 0.99 (2), H.·Cg2 2.80 (2) and C.·Cg2 3.785 (2) Å, and C—H···Cg2 175 (1)°; Cg2 is the centroid of the terminal aromatic ring, C8—C13], and this seems to influence the crystal packing (Fig. 2). In addition to these, van der Waals interactions also determine the crystal packing.

S2. Experimental

The title compound was obtained from the sodium salt of cumene hydroperoxide and 1,4-dibromoxylylene under phase-transfer catalysis conditions, similar to the method previously described by Zawadiak et al. (2001). The detailed synthetic procedure, together with the thermal behaviour of the compound, will be published elsewhere. Appropriate crystals of (I) were obtained by crystallization from a solution in hexane. The crystals were stored in the fridge in order to limit the slow decomposition of (I) at room temperature.

S3. Refinement

The choice of the non-standard space group I2/a (instead of C2/c) was caused by the large value of the β angle in the latter case [123.29 (1)°]. H atoms were refined freely.

Computing details

Data collection: KM-4 Software (Kuma Diffraction, 1991); cell refinement: KM-4 Software; data reduction: KM-4 Software; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 1997); software used to prepare material for publication: SHELXTL.

Figures

Fig. 1. A perspective view of two molecules of (I) connected via weak C—H···π interactions, which are drawn as dashed lines. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii. For clarity, the labels of the symmetry-related part of the molecule have been omitted.

1,4-Bis[(1-methyl-1-phenylethyl)peroxymethyl]benzene

Crystal data

C26H30O4	F(000) = 872
Mr = 406.50	Dx = 1.221 Mg m^−3
Monoclinic, I2/a	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -I 2ya	Cell parameters from 94 reflections
a = 15.368 (3) Å	θ = 3.2–16.7°
b = 6.2200 (12) Å	µ = 0.08 mm^−1
c = 23.142 (5) Å	T = 295 K
β = 90.44 (3)°	Block, colourless
V = 2212.1 (8) Å^3	0.4 × 0.3 × 0.2 mm
Z = 4

Data collection

Kuma KM-4 diffractometer	Rint = 0.012
Radiation source: fine-focus sealed tube	θmax = 25.1°, θmin = 2.7°
Graphite monochromator	h = −18→18
ω/2θ scans	k = 0→7
2007 measured reflections	l = 0→27
1951 independent reflections	3 standard reflections every 100 reflections
1198 reflections with I > 2σ(I)	intensity decay: 0.6%

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.033	All H-atom parameters refined
wR(F^2) = 0.092	w = 1/[σ^2(Fo^2) + (0.0551P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.01	(Δ/σ)max < 0.001
1951 reflections	Δρmax = 0.14 e Å^−3
197 parameters	Δρmin = −0.15 e Å^−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0123 (10)

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
C1	0.82024 (10)	0.8445 (3)	0.22393 (6)	0.0528 (4)
C2	0.82748 (9)	0.6366 (2)	0.24379 (5)	0.0491 (4)
C3	0.75619 (11)	0.5431 (3)	0.27037 (6)	0.0526 (4)
H3	0.7605 (10)	0.394 (3)	0.2842 (6)	0.059 (4)*
H1	0.8693 (11)	0.911 (3)	0.2058 (7)	0.062 (5)*
C4	0.90842 (11)	0.5088 (3)	0.23400 (7)	0.0620 (5)
H41	0.9201 (11)	0.404 (3)	0.2660 (7)	0.076 (5)*
H42	0.9611 (12)	0.602 (3)	0.2294 (7)	0.068 (5)*
C5	0.86717 (9)	0.3889 (2)	0.08673 (5)	0.0459 (4)
C6	0.92672 (11)	0.1994 (3)	0.07597 (9)	0.0636 (5)
H61	0.9150 (11)	0.134 (3)	0.0386 (8)	0.071 (5)*
H62	0.9900 (14)	0.249 (3)	0.0735 (7)	0.080 (5)*
H63	0.9242 (12)	0.098 (3)	0.1057 (8)	0.077 (6)*
C7	0.87333 (12)	0.5495 (3)	0.03790 (7)	0.0596 (5)
H71	0.9322 (13)	0.598 (3)	0.0314 (7)	0.082 (6)*
H72	0.8361 (12)	0.681 (3)	0.0453 (7)	0.074 (5)*
H73	0.8541 (12)	0.482 (3)	0.0013 (9)	0.084 (6)*
C8	0.77260 (9)	0.3268 (2)	0.09644 (5)	0.0426 (4)
C9	0.71600 (9)	0.4730 (3)	0.12117 (6)	0.0476 (4)
H9	0.7369 (9)	0.609 (3)	0.1336 (6)	0.055 (4)*
C10	0.62917 (10)	0.4243 (3)	0.12827 (7)	0.0570 (4)
H10	0.5921 (11)	0.531 (3)	0.1447 (7)	0.064 (5)*
C11	0.59709 (10)	0.2288 (3)	0.11074 (7)	0.0633 (5)
H11	0.5365 (12)	0.196 (3)	0.1163 (7)	0.074 (5)*
C12	0.65172 (11)	0.0822 (3)	0.08615 (8)	0.0647 (5)
H12	0.6295 (11)	−0.057 (3)	0.0731 (7)	0.072 (5)*
C13	0.73905 (10)	0.1310 (3)	0.07901 (7)	0.0552 (4)
H13	0.7759 (10)	0.031 (3)	0.0621 (7)	0.065 (5)*
O1	0.90193 (7)	0.36694 (17)	0.18551 (4)	0.0563 (3)
O2	0.89938 (6)	0.51176 (16)	0.13499 (4)	0.0493 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0569 (10)	0.0576 (10)	0.0442 (8)	−0.0102 (8)	0.0080 (7)	−0.0021 (8)
C2	0.0558 (9)	0.0539 (10)	0.0376 (7)	0.0010 (8)	−0.0019 (6)	−0.0046 (7)
C3	0.0700 (10)	0.0449 (9)	0.0428 (8)	−0.0026 (8)	0.0019 (7)	0.0008 (7)
C4	0.0581 (10)	0.0785 (12)	0.0493 (9)	0.0085 (10)	−0.0074 (7)	−0.0058 (9)
C5	0.0425 (7)	0.0509 (9)	0.0443 (7)	0.0013 (7)	0.0035 (6)	−0.0076 (7)
C6	0.0512 (11)	0.0709 (13)	0.0688 (12)	0.0144 (9)	0.0060 (8)	−0.0143 (11)
C7	0.0600 (11)	0.0664 (12)	0.0523 (10)	−0.0070 (9)	0.0097 (8)	0.0024 (9)
C8	0.0423 (7)	0.0451 (8)	0.0404 (7)	0.0015 (7)	−0.0003 (5)	0.0029 (6)
C9	0.0429 (8)	0.0527 (10)	0.0472 (8)	0.0035 (7)	−0.0016 (6)	−0.0032 (7)
C10	0.0423 (8)	0.0776 (12)	0.0511 (8)	0.0087 (9)	0.0009 (6)	0.0010 (9)
C11	0.0427 (9)	0.0832 (13)	0.0638 (10)	−0.0099 (9)	−0.0035 (8)	0.0123 (10)
C12	0.0603 (10)	0.0580 (11)	0.0756 (11)	−0.0168 (9)	−0.0099 (8)	0.0079 (9)
C13	0.0564 (10)	0.0460 (10)	0.0630 (9)	0.0018 (8)	−0.0006 (7)	−0.0013 (8)
O1	0.0611 (7)	0.0586 (7)	0.0490 (6)	0.0124 (5)	−0.0019 (4)	0.0005 (5)
O2	0.0456 (6)	0.0554 (6)	0.0469 (6)	−0.0045 (5)	0.0023 (4)	−0.0017 (5)

Geometric parameters (Å, º)

C1—C3^i	1.374 (2)	C6—H63	0.94 (2)
C1—C2	1.377 (2)	C7—H71	0.966 (19)
C1—H1	0.959 (17)	C7—H72	1.013 (19)
C2—C3	1.388 (2)	C7—H73	0.99 (2)
C2—C4	1.495 (2)	C8—C13	1.382 (2)
C3—C1^i	1.374 (2)	C8—C9	1.385 (2)
C3—H3	0.982 (17)	C9—C10	1.379 (2)
C4—O1	1.4303 (19)	C9—H9	0.951 (17)
C4—H41	1.002 (18)	C10—C11	1.372 (3)
C4—H42	1.002 (18)	C10—H10	0.956 (17)
C5—O2	1.4381 (16)	C11—C12	1.366 (3)
C5—C7	1.512 (2)	C11—H11	0.962 (18)
C5—C6	1.514 (2)	C12—C13	1.387 (2)
C5—C8	1.5220 (19)	C12—H12	0.979 (18)
C6—H61	0.972 (18)	C13—H13	0.930 (16)
C6—H62	1.02 (2)	O1—O2	1.4761 (13)
C3^i—C1—C2	120.84 (15)	C5—C7—H71	112.7 (10)
C3^i—C1—H1	119.9 (10)	C5—C7—H72	111.7 (9)
C2—C1—H1	119.3 (10)	H71—C7—H72	107.8 (15)
C1—C2—C3	118.63 (14)	C5—C7—H73	109.8 (11)
C1—C2—C4	120.94 (15)	H71—C7—H73	105.9 (14)
C3—C2—C4	120.33 (15)	H72—C7—H73	108.8 (15)
C1^i—C3—C2	120.52 (15)	C13—C8—C9	117.72 (14)
C1^i—C3—H3	120.3 (9)	C13—C8—C5	122.35 (13)
C2—C3—H3	119.2 (9)	C9—C8—C5	119.87 (13)
O1—C4—C2	113.19 (12)	C10—C9—C8	121.09 (16)
O1—C4—H41	101.0 (10)	C10—C9—H9	119.0 (9)
C2—C4—H41	112.2 (10)	C8—C9—H9	119.9 (9)
O1—C4—H42	109.0 (9)	C11—C10—C9	120.34 (17)
C2—C4—H42	112.4 (10)	C11—C10—H10	121.3 (10)
H41—C4—H42	108.3 (13)	C9—C10—H10	118.4 (10)
O2—C5—C7	101.89 (13)	C12—C11—C10	119.58 (16)
O2—C5—C6	109.67 (13)	C12—C11—H11	120.9 (10)
C7—C5—C6	110.49 (14)	C10—C11—H11	119.5 (10)
O2—C5—C8	110.09 (10)	C11—C12—C13	120.13 (18)
C7—C5—C8	110.08 (12)	C11—C12—H12	120.4 (10)
C6—C5—C8	113.95 (14)	C13—C12—H12	119.5 (10)
C5—C6—H61	111.3 (10)	C8—C13—C12	121.14 (16)
C5—C6—H62	110.6 (11)	C8—C13—H13	119.1 (10)
H61—C6—H62	104.2 (13)	C12—C13—H13	119.7 (10)
C5—C6—H63	112.1 (11)	C4—O1—O2	104.26 (11)
H61—C6—H63	111.4 (15)	C5—O2—O1	107.32 (10)
H62—C6—H63	106.8 (14)

Symmetry code: (i) −x+3/2, −y+3/2, −z+1/2.